{"id":22362,"date":"2026-07-16T12:32:07","date_gmt":"2026-07-16T12:32:07","guid":{"rendered":"https:\/\/www.sysinfotools.com\/blog\/?p=22362"},"modified":"2026-11-04T06:04:24","modified_gmt":"2026-11-04T06:04:24","slug":"legacy-imap-postfix-dovecot-to-microsoft-365-migration","status":"publish","type":"post","link":"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/","title":{"rendered":"Legacy IMAP (Postfix\/Dovecot) to Microsoft 365 Migration Guide"},"content":{"rendered":"<div class=\"p-4 mb-4\" style=\"border: 2px solid #005EFF; border-radius: 30px;\">\n<p><em><span style=\"font-weight: 400;\">\u201cWe have around 3 mailboxes between 30 and 70 GB that we want to migrate from the current local postfix\/dovecot IMAP server to Microsoft 365. We know that Microsoft has native tools for this migration, but we don\u2019t have licences. I came across MigrationWiz too, but we\u2019ve not been able to establish other best-in-class, cost-friendly competitors for that SaaS. Any suggestions and recommendations for this migration will be appreciated.\u201d<\/span><\/em><\/p>\n<p style=\"text-align: right;\"><strong>-Community Queries<\/strong><\/p>\n<\/div>\n<div class=\"block_sum\">\n<p>The migration of email systems is considered a critical undertaking for enterprises with large volumes. This is especially true for organizations planning a legacy IMAP (Postfix\/Dovecot) to Microsoft 365 migration. This technical guide elaborates on comprehensive solutions for the migration, either free or with the <strong>SysInfo <\/strong><a href=\"https:\/\/www.sysinfotools.com\/imap-email-backup.php\" target=\"_blank\" rel=\"noopener\"><strong>IMAP Backup Tool<\/strong><\/a>. Collaboration, security, and scalability present in Microsoft 365 make it a good option for shifting from on-premises IMAP systems. But the essential thing in this process is proper planning and implementation of the data transfer so that no data loss occurs.<\/p>\n<div class=\"blog-btn\">\n    <ul id=\"db-btn-container\" class=\"nav nav-tabs mt-4\" role=\"tablist\">\n\n        <li class=\"nav-item\">\n            <a id=\"windows-tab\" class=\"nav-link active\" role=\"tab\" href=\"#windows\" data-toggle=\"tab\" aria-controls=\"windows\" aria-selected=\"true\">\n                <i class=\"icon-windows\"><\/i> Windows\n            <\/a>\n        <\/li>\n\n        <li class=\"nav-item\">\n            <a id=\"mac-tab\" class=\"nav-link\" role=\"tab\" href=\"#mac\" data-toggle=\"tab\" aria-controls=\"mac\" aria-selected=\"false\">\n                <i class=\"icon-apple\"><\/i> Mac\n            <\/a>\n        <\/li>\n\n        <li class=\"nav-item\">\n            <a id=\"linux-tab\" class=\"nav-link\" role=\"tab\" href=\"#linux\" data-toggle=\"tab\" aria-controls=\"linux\" aria-selected=\"false\">\n                <i class=\"icon-linux\"><\/i> Linux\n            <\/a>\n        <\/li>\n\n    <\/ul>\n    <div id=\"db-btn-containerContent\" class=\"tab-content my-2\">\n        <div id=\"windows\" class=\"tab-pane fade active show\" role=\"tabpanel\" aria-labelledby=\"windows-tab\">\n            <a class=\"sum-d-btn\" href=\"https:\/\/www.sysinfotools.com\/imap-email-backup.php\" target=\"_blank\">\n                <i class=\"icon-windows\"><\/i> Download Now\n            <\/a>\n        <\/div>\n        <div id=\"mac\" class=\"tab-pane fade\" role=\"tabpanel\" aria-labelledby=\"mac-tab\">\n            <a class=\"sum-d-btn\" href=\"https:\/\/www.sysinfotools.com\/imap-email-backup.php\" target=\"_blank\">\n                <i class=\"icon-apple\"><\/i> Download Now\n            <\/a>\n        <\/div>\n        <div id=\"linux\" class=\"tab-pane fade\" role=\"tabpanel\" aria-labelledby=\"linux-tab\">\n            <a class=\"sum-d-btn\" href=\"https:\/\/www.sysinfotools.com\/imap-email-backup.php\" target=\"_blank\">\n                <i class=\"icon-linux\"><\/i> Download Now\n            <\/a>\n        <\/div>\n    <\/div>\n<\/div>\n<\/div>\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_89 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<div class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/div>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#Why_Legacy_PostfixDovecot_Mailboxes_to_Microsoft_365_Migration\" >Why Legacy Postfix\/Dovecot Mailboxes to Microsoft 365 Migration?<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#How_to_Simplify_Legacy_IMAP_PostfixDovecot_to_Microsoft_365_Migration\" >How to Simplify Legacy IMAP (Postfix\/Dovecot) to Microsoft 365 Migration?<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#Checklist_for_PostfixDovecot_Migration_to_M365\" >Checklist for Postfix\/Dovecot Migration to M365<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#Manual_Legacy_IMAP_PostfixDovecot_to_Microsoft_365_Migration\" >Manual Legacy IMAP (Postfix\/Dovecot) to Microsoft 365 Migration<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#Why_is_Manual_Migration_Less_Preferred_What_to_Troubleshoot\" >Why is Manual Migration Less Preferred? What to Troubleshoot?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#Smart_Legacy_IMAP_PostfixDovecot_to_Microsoft_365_Migration\" >Smart Legacy IMAP (Postfix\/Dovecot) to Microsoft 365 Migration<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#Who_Needs_This_Legacy_PostfixDovecot_Mailboxes_to_Microsoft_365_Migration\" >Who Needs This Legacy Postfix\/Dovecot Mailboxes to Microsoft 365 Migration?<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#Ending_Remarks\" >Ending Remarks\u00a0<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n<h2><span class=\"ez-toc-section\" id=\"Why_Legacy_PostfixDovecot_Mailboxes_to_Microsoft_365_Migration\"><\/span>Why Legacy Postfix\/Dovecot Mailboxes to Microsoft 365 Migration?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Legacy IMAP servers such as Postfix and Dovecot served their purpose for several years, offering robust email services. With easy setup, lightweight design, open-source service, and high performance, it was used by numerous businesses on Linux\/Unix OS. It supports Maildir and MBOX formats to work along well with Outlook or Thunderbird, but command-line configurations aren\u2019t suitable everywhere.\u00a0<\/p>\n<p>However, when organizations required scalability, reliability, efficiency, advanced security, integration with modern productivity and collaboration tools, and AI access, they were limited. Microsoft 365 proves to be useful in all of it as:<\/p>\n<ul>\n<li>Threat protection, spam detection, data loss prevention, compliance features, and MFA abilities.\u00a0<\/li>\n<li>Developed on cloud-based infrastructure that provides easy scaling and high availability, meeting current business needs.\u00a0<\/li>\n<li>Works well along with Outlook, Teams, SharePoint, OneDrive, Word, Excel, and other applications.\u00a0<\/li>\n<li>IT overheads are generally reduced due to managed services with central administration.\u00a0<\/li>\n<li>Server maintenance, backups, and patches are all maintained while ensuring secure data transfers.\u00a0<\/li>\n<li>Easily accessible anytime and anywhere. Even offers Copilot AI for smart search and task automation.\u00a0<\/li>\n<li>Preserves business domain brand consistency and improves professionalism.\u00a0<\/li>\n<li>Handles large and bulky email volumes and attachments without risks, unlike Dovecot.\u00a0<\/li>\n<\/ul>\n<table border=\"1\">\n<tbody>\n<tr>\n<td>\n<h3><span class=\"ez-toc-section\" id=\"How_to_Simplify_Legacy_IMAP_PostfixDovecot_to_Microsoft_365_Migration\"><\/span>How to Simplify Legacy IMAP (Postfix\/Dovecot) to Microsoft 365 Migration?<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>To simplify your tasks, using the manual method of migration is always challenging. Instead, use the <strong>IMAP Email Backup Software<\/strong>, which supports delta migration and ensures secure OAuth 2.0 authentication. It is smooth, well-managed, and saves your precious time for critical large-scale migrations with a clear interface and 5 simple steps for disruption-free mailbox migration. These are:<\/p>\n<ol>\n<li>Launch the <strong>dedicated converter software<\/strong> to begin <strong>IMAP migration<\/strong>.\u00a0<\/li>\n<li><strong>Sign in<\/strong> to your <strong>Postfix account<\/strong> and click the <strong>Continue<\/strong> button.\u00a0<\/li>\n<li>Choose the <strong>email folders<\/strong> to transfer and click <strong>Next<\/strong> to select<strong> M365.\u00a0<\/strong><\/li>\n<li><strong>Sign in <\/strong>to your <strong>Microsoft 365<\/strong> account via modern authentication.\u00a0<\/li>\n<li>Finally, pick the <strong>filters<\/strong> to apply for customization and tap<strong> Next<\/strong> to migrate.\u00a0<\/li>\n<\/ol>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2><span class=\"ez-toc-section\" id=\"Checklist_for_PostfixDovecot_Migration_to_M365\"><\/span>Checklist for Postfix\/Dovecot Migration to M365<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Before the actual migration, you must ensure a few things, including:<\/p>\n<ul>\n<li>Choose whether to retain your Dovecot server domain or shift to another provider.\u00a0<\/li>\n<li>Identify whether you want to migrate the entire dataset at once or in batches.\u00a0<\/li>\n<li>Prepare a CSV with a list of all mailboxes and verify that all credentials are correct.\u00a0<\/li>\n<li>Remove unnecessary mailboxes from the source and notify end users of the migration plan.\u00a0<\/li>\n<li>Select appropriate Office 365 Exchange Online licences and assign them to the specific users.\u00a0<\/li>\n<li>Set up your Microsoft 365 account properly and prepare user accounts for all mailboxes.\u00a0<\/li>\n<li>For the same domain, add and verify it in the Microsoft 365 target tenant before assigning the users.\u00a0<\/li>\n<li>Secure the IMAP name and access from the internet, allowing connections with M365.\u00a0<\/li>\n<li>Adjust rules for the firewall, antivirus, or connection limits to improve the migration.\u00a0<\/li>\n<li>Ensure you have either passwords or admin access for all user mailboxes to be accessed.\u00a0<\/li>\n<li>Prepare a complete backup of your Postfix\/Dovecot server before the migration.\u00a0<\/li>\n<li>Check your internet connectivity and have access to the M365 Admin Center.\u00a0<\/li>\n<li>Disable all MRM and archival policies as recommended by Microsoft to prevent messages from being marked flagged or missing, i.e., data loss.\u00a0<\/li>\n<\/ul>\n<p>Once you understand and fulfil all these prerequisites, proceeding with the migration becomes a little simpler.\u00a0<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Manual_Legacy_IMAP_PostfixDovecot_to_Microsoft_365_Migration\"><\/span>Manual Legacy IMAP (Postfix\/Dovecot) to Microsoft 365 Migration<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Even though the process here may vary slightly depending on your environment and method opted for, the general workflow is the same. The steps to follow are:<\/p>\n<ol>\n<li>\n<h4>Preparing Environment\u00a0<\/h4>\n<p>It is the first foundational step for a proper migration. Here, ensure that all <strong>user mailboxes<\/strong> are created in M365 and have <strong>assigned licences<\/strong>. Also, verify that your <strong>domain is configured<\/strong> with M365.\u00a0<\/p>\n<\/li>\n<li>\n<h4>Identifying IMAP Server Details\u00a0<\/h4>\n<p>Locate the complete <strong>IMAP Server (:\/\/yourdomain.com) <\/strong>and<strong> port of your Postfix\/Dovecot <\/strong>account. It is essential that your M365 connects well with the source account. Locate it in your email client settings or consult your server admin to provide the same.\u00a0<\/p>\n<\/li>\n<li>\n<h4>Creating CSV File for Batch Migration<\/h4>\n<p>When you need to migrate multiple accounts altogether, using a <strong>CSV (Comma-Separated Value) file <\/strong>is an ideal choice. The structure of your CSV must have these columns:<\/p>\n<table>\n<tbody>\n<tr>\n<td>\n<p><strong>Email Address (Postfix\/Dovecot)<\/strong><\/p>\n<\/td>\n<td>\n<p><strong>Username (Office 365)<\/strong><\/p>\n<\/td>\n<td>\n<p><strong>Password (O365 Associated)<\/strong><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/li>\n<li>\n<h4>Connecting Source and Target Servers\u00a0<\/h4>\n<p>This step requires you to create <strong>migration endpoints <\/strong>in the <strong>Exchange Admin Center<\/strong>, defining the settings needed to connect the accounts. Follow these:<\/p>\n<ul>\n<li><strong>Sign in<\/strong> to your <strong>Microsoft 365 Admin account<\/strong>.\u00a0<\/li>\n<li>Then, open <strong>Exchange Admin Center <\/strong>and move to the <strong>Migration<\/strong> tab.\u00a0<\/li>\n<li>Choose <strong>Endpoints <\/strong>and click the <strong>Add<\/strong> button. Choose <strong>IMAP<\/strong> from the menu.\u00a0<\/li>\n<li>Further, enter the<strong> required credentials<\/strong> and leave the rest of the settings at the default. Lastly, click<strong> Create<\/strong>.\u00a0<\/li>\n<\/ul>\n<\/li>\n<li>\n<h4>Prepare the Migration Batch &amp; Proceed\u00a0<\/h4>\n<p>This process involves <strong>preparing batches<\/strong> once the endpoints are configured. You may need the<strong> CSV file<\/strong> created earlier at this step. It is a critical step where you can even monitor your progress, errors, and warnings. Steps are:<\/p>\n<ul>\n<li>Initially, move back to the<strong> EAC<\/strong> and, from <strong>Migration<\/strong>, click <strong>Add Migration Batch<\/strong>.\u00a0<\/li>\n<li>Next, provide it with a <strong>name<\/strong> and opt for \u201c<strong>Migrate to Exchange Online<\/strong>\u201d. Tap <strong>Next.<\/strong>\u00a0<\/li>\n<li>Further, pick <strong>IMAP migration<\/strong> as your type, click <strong>Next<\/strong>, and select the <strong>Migration Endpoint<\/strong> you created earlier.\u00a0<\/li>\n<li>Click <strong>Next<\/strong>, and in the <strong>Add User Mailboxes <\/strong>tab, upload the <strong>CSV<\/strong> you prepared earlier.\u00a0<\/li>\n<li>Again, tap <strong>Next<\/strong> and select the <strong>filtering options<\/strong> as desired in the configuration window.\u00a0<\/li>\n<li>Tap <strong>Next<\/strong> and choose to <strong>schedule your migration batch <\/strong>for completion. Click <strong>Save<\/strong>.<\/li>\n<\/ul>\n<\/li>\n<li>\n<h4>Update Records &amp; Additional Settings\u00a0<\/h4>\n<p>Once the mailboxes are migrated and verified, as you can check from the <strong>Migration Dashboard<\/strong> window, it\u2019s essential to redirect the email flow. Also, update your domain&#8217;s <strong>MX (Mail Exchanger) record,<\/strong> and it will ensure that all new incoming emails are routed to Microsoft 365 from Postfix\/Dovecot. Note that <strong>DNS changes<\/strong> take time to propagate, so plan accordingly. Once done, test your email flow, and if everything works, you may decommission the Postfix\/Dovecot server.\u00a0<\/p>\n<\/li>\n<\/ol>\n<p>This marks the completion of the native method to migrate from legacy IMAP (Postfix\/Dovecot) to Microsoft 365. However, it is obviously not that simple and contains several loopholes.\u00a0<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Why_is_Manual_Migration_Less_Preferred_What_to_Troubleshoot\"><\/span>Why is Manual Migration Less Preferred? What to Troubleshoot?<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Users often face multiple complexities during the free migration without any professional utility. This is what you must know:\u00a0<\/p>\n<ul>\n<li>Mailboxes show errors \u2192 check your credentials, port, and encryption<\/li>\n<li>Contacts and calendars aren\u2019t available \u2192 export ICS\/vCard manually<\/li>\n<li>Delays post-cutover \u2192 wait for DNS syncs to complete (48-72hrs)<\/li>\n<li>Access denied at endpoints (IMAP) \u2192 check user\/admin credentials<\/li>\n<li>Oversized migration issues \u2192 split migration in batches or retry migration<\/li>\n<li>Cannot connect to the server \u2192 verify internet network connectivity\u00a0<\/li>\n<li>Throttle concurrent connections \u2192 divide in small batches\u00a0<\/li>\n<\/ul>\n<p>Some other limitations that must be considered are:<\/p>\n<ul>\n<li>Time-consuming process that requires effort and technical skills<\/li>\n<li>Users must have proper admin credentials\u00a0<\/li>\n<li>Skipping any step can result in starting the entire migration from scratch<\/li>\n<\/ul>\n<h3><span class=\"ez-toc-section\" id=\"Smart_Legacy_IMAP_PostfixDovecot_to_Microsoft_365_Migration\"><\/span>Smart Legacy IMAP (Postfix\/Dovecot) to Microsoft 365 Migration<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>When you are planning to <a href=\"https:\/\/www.sysinfotools.com\/blog\/migrate-dovecot-to-new-server\/\" target=\"_blank\" rel=\"noopener\"><strong>migrate Dovecot to new server<\/strong><\/a> like Microsoft 365 or others, the most important thing is to ensure data is retained securely. SysInfo IMAP Backup Tool helps you with this by providing secure App Password\/Modern OAuth 2.0 or Assign Impersonation Authentication. Additionally, it lets all experts and novice users manage their large and bulky Postfix mailboxes with 100% accuracy and zero data loss. Moreover, with a simplified interface and easy-to-follow steps, this software eases migrating mailboxes between popular email clients, such as:<\/p>\n<ol>\n<li>Launch the <strong>IMAP Mail Migration Tool <\/strong>and click <strong>IMAP Migration<\/strong>.\u00a0<br \/><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-22375\" src=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/1-1.webp\" alt=\"Launch the IMAP Mail Migration Tool and click IMAP Migration\" width=\"751\" height=\"421\" srcset=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/1-1.webp 751w, https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/1-1-300x168.webp 300w\" sizes=\"auto, (max-width: 751px) 100vw, 751px\" \/><\/li>\n<li>With <strong>Single\/Batch<\/strong> login, sign in to your<strong> Postfix\/Dovecot<\/strong> account.\u00a0<br \/><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-22376\" src=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/2-1.webp\" alt=\"Single\/Batch login, sign in to your Postfix\/Dovecot account\" width=\"751\" height=\"421\" srcset=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/2-1.webp 751w, https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/2-1-300x168.webp 300w\" sizes=\"auto, (max-width: 751px) 100vw, 751px\" \/><\/li>\n<li>Then, choose the <strong>folders<\/strong> to migrate and click <strong>Continue to Filters.<\/strong>\u00a0<br \/><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-22377\" src=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/3-1.webp\" alt=\"choose the folders to migrate and click Continue to Filters\" width=\"751\" height=\"421\" srcset=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/3-1.webp 751w, https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/3-1-300x168.webp 300w\" sizes=\"auto, (max-width: 751px) 100vw, 751px\" \/><\/li>\n<li>Further, select <strong>Office 365 <\/strong>from the destination and <strong>sign in<\/strong> to your account.\u00a0<br \/><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-22378\" src=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/4-1.webp\" alt=\"select Office 365 from the destination and sign in to your account\" width=\"751\" height=\"421\" srcset=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/4-1.webp 751w, https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/4-1-300x168.webp 300w\" sizes=\"auto, (max-width: 751px) 100vw, 751px\" \/><\/li>\n<li>Afterward, opt for all the desired filter options and click <strong>Next<\/strong> to migrate.<br \/><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-22379\" src=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/5-1.webp\" alt=\"opt for all the desired filter options and click Next to migrate\" width=\"751\" height=\"421\" srcset=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/5-1.webp 751w, https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/5-1-300x168.webp 300w\" sizes=\"auto, (max-width: 751px) 100vw, 751px\" \/><\/li>\n<li>Finally, the migration is initiated. Wait until the process marks complete.\u00a0<br \/><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-22380\" src=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/6-1.webp\" alt=\"Finally, the migration is initiated. Wait until the process marks complete\" width=\"751\" height=\"421\" srcset=\"https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/6-1.webp 751w, https:\/\/www.sysinfotools.com\/blog\/wp-content\/uploads\/2026\/07\/6-1-300x168.webp 300w\" sizes=\"auto, (max-width: 751px) 100vw, 751px\" \/><\/li>\n<\/ol>\n<h4>How Does the Software Ensure a Flawless Migration?<\/h4>\n<ul>\n<li>Allows users to <a href=\"https:\/\/www.sysinfotools.com\/blog\/migrate-dovecot-to-office-365\/\" target=\"_blank\" rel=\"noopener\"><strong>migrate Dovecot to Office 365<\/strong><\/a> effortlessly\u00a0<\/li>\n<li>Saves time with an automated process without much hassle\u00a0<\/li>\n<li>Allows easy mapping for multiple accounts and direct transfers\u00a0<\/li>\n<li>Handles original Postfix\/Dovecot mailbox data with utmost precision\u00a0<\/li>\n<li>Provides a demo version for software evaluation beforehand\u00a0<\/li>\n<li>Works smoothly across all versions of Windows and Mac OS<\/li>\n<\/ul>\n<div style=\"background: linear-gradient(135deg, #fafdff, #ddf2ff); border-left: 5px solid #1e4258; border-radius: 12px; padding: 20px 25px; margin: 15px 0px; box-shadow: rgba(0, 0, 0, 0.08) 0px 4px 14px; transition: 0.3s; font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; color: #2a2a2a;\">\n<p><strong>Example Case:<\/strong>\u00a0<\/p>\n<p>A mid-sized firm with 150-250 users in London needed to migrate their legacy email archives from 5 Postfix\/Dovecot servers over IMAP to Microsoft 365. They had admin credentials and prepared the entire Exchange Admin Migration process, but it failed midway, and they needed it to be done urgently. At short notice, they bought the SysInfo IMAP Mail Migrator and used it for their Postfix\/Dovecot to M365 migration. In some while, all their emails were transferred accurately with no loss or downtime. The folder structures were preserved, and users continued working without disruption of business operations.\u00a0<\/p>\n<\/div>\n<h2><span class=\"ez-toc-section\" id=\"Who_Needs_This_Legacy_PostfixDovecot_Mailboxes_to_Microsoft_365_Migration\"><\/span>Who Needs This Legacy Postfix\/Dovecot Mailboxes to Microsoft 365 Migration?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>With systematic shifts in businesses, the demand for migration shifts too. It depends on how your business communicates, collaborates, and manages IT security. Usually, this falls into the top 3 categories as stated here:\u00a0<\/p>\n<table border=\"1\">\n<tbody>\n<tr>\n<td>\n<p><strong>Growing Large-Scale Organizations &amp; Enterprises\u00a0<\/strong><\/p>\n<p>&nbsp;<\/p>\n<ul>\n<li>Teams who require more collaboration than just email exchange, like access to shared Outlook calendars, contacts, and real-time documents on OneDrive and SharePoint.\u00a0<\/li>\n<li>Those who are working with disjointed workspaces and want to shift to a single unified ecosystem.\u00a0<\/li>\n<li>Users who need access to applications on their Android mobiles and iOS simultaneously.\u00a0<\/li>\n<\/ul>\n<\/td>\n<td>\n<p><strong>IT Teams Facing Maintenance Overheads<\/strong><\/p>\n<p>&nbsp;<\/p>\n<ul>\n<li>Admins who do not want to fix the physical Linux servers, RAID arrays, and hardware cycles anymore, or manage storage quotas of the Dovecot infrastructure.\u00a0<\/li>\n<li>Teams who need to reduce the costs spent on preventing malware, phishing, and ransomware attacks with adoption of Microsoft Defender.\u00a0<\/li>\n<li>Individuals avoiding downtime and operational risks with Microsoft uptime Service Level Agreement (SLA).\u00a0<\/li>\n<\/ul>\n<\/td>\n<td>\n<p><strong>Businesses Focused on Legal Regulations\u00a0<\/strong><\/p>\n<p>&nbsp;<\/p>\n<ul>\n<li>Organizations planning to comply with all the industry and legal standards and policies in multiple sectors like GDPR, HIPAA, SOC 2, etc.\u00a0<\/li>\n<li>Businesses in need of achieving the Data Loss Prevention (Litigation Holds) and eDiscovery tools as available by M365.\u00a0<\/li>\n<li>Firms requiring modern authentication and more robust data security like Microsoft\u2019s Multi-Factor Authentication (MFA) and Conditional Access Policies.\u00a0<\/li>\n<\/ul>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h3><span class=\"ez-toc-section\" id=\"Ending_Remarks\"><\/span>Ending Remarks\u00a0<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Only the use of the right solution can enable a secure legacy IMAP (Postfix\/Dovecot) to Microsoft 365 migration. It is a strategic move to enhance data security and access interactive productivity and collaboration tools at enterprise scale with ease. Thus, reducing IT overheads and technical complexities of the outdated servers. Remember that this process requires careful planning and execution, a structured method, predefined and fulfilled prerequisites, and knowledge of the limitations. With correct and expert trusted solutions like SysInfo IMAP Email Backup Software, one can easily achieve successful migrations. Later, leveraging M365 capabilities in their workplace to empower productivity.<\/p>\n<h4 class=\"faq_heading\">Frequently Asked Questions<\/h4>\n\n\n<div class=\"schema-faq wp-block-yoast-faq-block\"><div class=\"schema-faq-section\" id=\"faq-question-1784204139490\"><strong class=\"schema-faq-question\">Q1. Will my folder structure remain the same after migration?<\/strong> <p class=\"schema-faq-answer\"><strong>Ans. <\/strong>Indeed, the folder hierarchy of your mailboxes is generally retained in an IMAP (Postfix\/Dovecot) to Office 365 migration. All the folders will be recreated in Microsoft 365 automatically, preserving the organization you had on the Postfix\/Dovecot mail server.\u00a0<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1784204169156\"><strong class=\"schema-faq-question\">Q2. What data is migrated from a Legacy IMAP server?<\/strong> <p class=\"schema-faq-answer\"><strong>Ans. <\/strong>IMAP migrations are mainly concerned with transferring emails and folders associated with the specific mail account. It is important to understand that contacts, calendars, tasks, and notes are usually not transported in a standard IMAP migration. For such elements, consider using a dedicated solution.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1784204188332\"><strong class=\"schema-faq-question\">Q3. How long does the Legacy IMAP (Postfix\/Dovecot) to Microsoft 365 migration take?<\/strong> <p class=\"schema-faq-answer\"><strong>Ans. <\/strong>The time the migration from IMAP (Postfix\/Dovecot) to Microsoft 365 takes is determined by several factors, including the size of the data, the number of mailboxes, the speed of your internet connection, and the performance of the source IMAP server. Microsoft 365 imposes limitations, such as the fact that there cannot be more than 500,000 items in one mail account, while the maximum size of the email is 35 MB. As such, it is a good idea to perform large migrations in batches and during off-peak hours or use the professional IMAP Backup Software by SysInfo.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1784204206125\"><strong class=\"schema-faq-question\">Q4. What are the prerequisites for IMAP migration?<\/strong> <p class=\"schema-faq-answer\"><strong>Ans. <\/strong>A well-established\u00a0 Microsoft 365 tenant with assigned licensed users, details of the source IMAP server, and the credentials needed for access to the mailbox. Disabled MRM and archiving policies on the source side are advised too. For more specific details, check out the prerequisites section as provided above.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1784204223819\"><strong class=\"schema-faq-question\">Q5. Is Legacy Postfix\/Dovecot Mailboxes to Microsoft 365 Migration suitable for businesses?<\/strong> <p class=\"schema-faq-answer\"><strong>Ans. <\/strong>Certainly, migrating from Legacy Postfix or Dovecot to Microsoft 365 is highly recommended for companies who wish to achieve modernization in their email infrastructure. Microsoft 365 offers a host of benefits, like increased security, scalability, reliability, and integration with numerous productivity tools for business.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1784204239628\"><strong class=\"schema-faq-question\">Q6. Is there any mailbox size limit during IMAP migration?<\/strong> <p class=\"schema-faq-answer\"><strong>Ans. <\/strong>Specifically, the maximum number of items (emails) that can be transferred from one mailbox to another is 500,000, and the maximum size of one email is 35 MB. In case the mailbox is larger than this, it may be necessary to opt for a software or run small migration batches with optimal file size.<\/p> <\/div> <\/div>\n\n\n<div class=\"kk-star-ratings kksr-auto kksr-align-left kksr-valign-bottom\"\n    data-payload='{&quot;align&quot;:&quot;left&quot;,&quot;id&quot;:&quot;22362&quot;,&quot;slug&quot;:&quot;default&quot;,&quot;valign&quot;:&quot;bottom&quot;,&quot;ignore&quot;:&quot;&quot;,&quot;reference&quot;:&quot;auto&quot;,&quot;class&quot;:&quot;&quot;,&quot;count&quot;:&quot;0&quot;,&quot;legendonly&quot;:&quot;&quot;,&quot;readonly&quot;:&quot;&quot;,&quot;score&quot;:&quot;0&quot;,&quot;starsonly&quot;:&quot;&quot;,&quot;best&quot;:&quot;5&quot;,&quot;gap&quot;:&quot;5&quot;,&quot;greet&quot;:&quot;Rate this post&quot;,&quot;legend&quot;:&quot;0\\\/5 - (0 votes)&quot;,&quot;size&quot;:&quot;24&quot;,&quot;title&quot;:&quot;Legacy IMAP (Postfix\\\/Dovecot) to Microsoft 365 Migration Guide&quot;,&quot;width&quot;:&quot;0&quot;,&quot;_legend&quot;:&quot;{score}\\\/{best} - ({count} {votes})&quot;,&quot;font_factor&quot;:&quot;1.25&quot;}'>\n            \n<div class=\"kksr-stars\">\n    \n<div class=\"kksr-stars-inactive\">\n            <div class=\"kksr-star\" data-star=\"1\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" data-star=\"2\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" data-star=\"3\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" data-star=\"4\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" data-star=\"5\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n    <\/div>\n    \n<div class=\"kksr-stars-active\" style=\"width: 0px;\">\n            <div class=\"kksr-star\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n    <\/div>\n<\/div>\n                \n\n<div class=\"kksr-legend\" style=\"font-size: 19.2px;\">\n            <span class=\"kksr-muted\">Rate this post<\/span>\n    <\/div>\n    <\/div>\n","protected":false},"excerpt":{"rendered":"<p>\u201cWe have around 3 mailboxes between 30 and 70 GB that we want to migrate from the current local postfix\/dovecot<a class=\"read-more ml-1 main-read-more\" href=\"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/\">Read More<\/a><\/p>\n","protected":false},"author":1,"featured_media":22374,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[528],"tags":[],"class_list":["post-22362","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-mail-management"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.6 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Legacy IMAP (Postfix\/Dovecot) to Microsoft 365 Migration Guide<\/title>\n<meta name=\"description\" content=\"Master Legacy IMAP to Microsoft 365 Migration with proven methods. Move Postfix\/Dovecot emails safely while preserving mailbox data.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Legacy IMAP (Postfix\/Dovecot) to Microsoft 365 Migration Guide\" \/>\n<meta property=\"og:description\" content=\"Master Legacy IMAP to Microsoft 365 Migration with proven methods. 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All the folders will be recreated in Microsoft 365 automatically, preserving the organization you had on the Postfix\/Dovecot mail server.\u00a0","inLanguage":"en-US"},"inLanguage":"en-US"},{"@type":"Question","@id":"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#faq-question-1784204169156","position":2,"url":"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#faq-question-1784204169156","name":"Q2. What data is migrated from a Legacy IMAP server?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"<strong>Ans. <\/strong>IMAP migrations are mainly concerned with transferring emails and folders associated with the specific mail account. It is important to understand that contacts, calendars, tasks, and notes are usually not transported in a standard IMAP migration. For such elements, consider using a dedicated solution.","inLanguage":"en-US"},"inLanguage":"en-US"},{"@type":"Question","@id":"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#faq-question-1784204188332","position":3,"url":"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#faq-question-1784204188332","name":"Q3. How long does the Legacy IMAP (Postfix\/Dovecot) to Microsoft 365 migration take?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"<strong>Ans. <\/strong>The time the migration from IMAP (Postfix\/Dovecot) to Microsoft 365 takes is determined by several factors, including the size of the data, the number of mailboxes, the speed of your internet connection, and the performance of the source IMAP server. Microsoft 365 imposes limitations, such as the fact that there cannot be more than 500,000 items in one mail account, while the maximum size of the email is 35 MB. As such, it is a good idea to perform large migrations in batches and during off-peak hours or use the professional IMAP Backup Software by SysInfo.","inLanguage":"en-US"},"inLanguage":"en-US"},{"@type":"Question","@id":"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#faq-question-1784204206125","position":4,"url":"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#faq-question-1784204206125","name":"Q4. What are the prerequisites for IMAP migration?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"<strong>Ans. <\/strong>A well-established\u00a0 Microsoft 365 tenant with assigned licensed users, details of the source IMAP server, and the credentials needed for access to the mailbox. Disabled MRM and archiving policies on the source side are advised too. For more specific details, check out the prerequisites section as provided above.","inLanguage":"en-US"},"inLanguage":"en-US"},{"@type":"Question","@id":"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#faq-question-1784204223819","position":5,"url":"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#faq-question-1784204223819","name":"Q5. Is Legacy Postfix\/Dovecot Mailboxes to Microsoft 365 Migration suitable for businesses?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"<strong>Ans. <\/strong>Certainly, migrating from Legacy Postfix or Dovecot to Microsoft 365 is highly recommended for companies who wish to achieve modernization in their email infrastructure. Microsoft 365 offers a host of benefits, like increased security, scalability, reliability, and integration with numerous productivity tools for business.","inLanguage":"en-US"},"inLanguage":"en-US"},{"@type":"Question","@id":"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#faq-question-1784204239628","position":6,"url":"https:\/\/www.sysinfotools.com\/blog\/legacy-imap-postfix-dovecot-to-microsoft-365-migration\/#faq-question-1784204239628","name":"Q6. Is there any mailbox size limit during IMAP migration?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"<strong>Ans. <\/strong>Specifically, the maximum number of items (emails) that can be transferred from one mailbox to another is 500,000, and the maximum size of one email is 35 MB. In case the mailbox is larger than this, it may be necessary to opt for a software or run small migration batches with optimal file size.","inLanguage":"en-US"},"inLanguage":"en-US"}]}},"_links":{"self":[{"href":"https:\/\/www.sysinfotools.com\/blog\/wp-json\/wp\/v2\/posts\/22362","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.sysinfotools.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.sysinfotools.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.sysinfotools.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.sysinfotools.com\/blog\/wp-json\/wp\/v2\/comments?post=22362"}],"version-history":[{"count":13,"href":"https:\/\/www.sysinfotools.com\/blog\/wp-json\/wp\/v2\/posts\/22362\/revisions"}],"predecessor-version":[{"id":23165,"href":"https:\/\/www.sysinfotools.com\/blog\/wp-json\/wp\/v2\/posts\/22362\/revisions\/23165"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.sysinfotools.com\/blog\/wp-json\/wp\/v2\/media\/22374"}],"wp:attachment":[{"href":"https:\/\/www.sysinfotools.com\/blog\/wp-json\/wp\/v2\/media?parent=22362"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.sysinfotools.com\/blog\/wp-json\/wp\/v2\/categories?post=22362"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.sysinfotools.com\/blog\/wp-json\/wp\/v2\/tags?post=22362"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}