What is Maildir File Format & Difference Between Maildir & Maildir++

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  • Published on
    April 28th, 2019
  • Updated on
    February 26, 2021
  • Read Time
    4 minutes
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Many email client application store their files in an offline form on the local windows PC so that the user can access them without internet access. Nowadays it is common among the various email applications. In this article, I will discuss one such format known as Maildir file format which is also saved by the email clients. The Maildir file stores various information about the emails. I know many of you are unaware of this file format.

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So in this article, I will explain what Maildir file format is.

Difference Between Maildir File and Maildir++

It is basically a file format which is used to store the messages of an email in a systematic form. It is created by Qmail email client, which is now very common these days. Even Mozilla Thunderbird uses this file format. A separate file is created in Maildir form with a unique name whenever the user receives any message.

Maildir++ is a file extension of Maildir files which supports subfolders and mail quotas. All the subdirectories in Maildir++ are found to be named as (dot) .thefilename. You will understand it better form the image given below:-

maildir file format

Maildir Directory Structure

You must have understood what is Maildir file? Now I will tell you the file structure of the Maildir file. Every email folders are categorized in the form of directories. The important ones are mentioned below:-

  • Tmp- It stores the temporary emails for the mailbox synced to the file.
  • New-All the unread messages are stored in this directory. It stores the email Return Path and Delivered to This information tells us the path taken by the emails which can be beneficial in tracing emails. Messages are received in RFC 822 format by the Maildir File Extension. It intact the text integrity and prevents leakage of data. All the records of modifications, edits, and date creation are kept in this directory.
  • Cur- The messages which are already read are kept in the Cur directory. All the read emails are stored in a well-structured form in this directory. The opened messages are kept separately in a different folder. So in the case of cyber-crime, the bureau can easily inspect the needed folder.

You will understand better once you’ll see the pictorial presentation of how the directory appears in front of you. You can see the image below:-

maildir and maildir++

How does a Maildir file looks like?

You can see in the image that how a Maildir file is displayed in front of you. But I am quite sure that you are unable to understand the code. Let’s see what the codes tell us.

what is maildir format

R (Read) Denotes that the user has read the message.

1463907228It is the Arrival Timestamp.
S=72605The Size of the Email Message.
Last SS (Seen) The user has seen the email message but haven’t read it.
Or RR (Read) Denotes that the user has read the message.
Or FF (Flagged) Specifies that the user has flagged that particular email Message.

Advantages of Maildir File Format

  • This file format if safe and there are minimal chances of file corruption.
  • Easy to share from one system to another.
  • Great Message Filtration according to their folders.
  • All the messages are saved according to their characteristics into the subfolders.
  • Any kind of cyber-crime can be detected easily with the help of its structured format.
  • Fast Search, Retrieval and Deletion of emails.

Compatibility of Maildir Files

  • Online Email Servers– Courier Mail Server, Exim, Dovecot, Qmail, Xmail.
  • Email Client Applications– Alpine, Mutt, Cone, Balsa, Pine, Thunderbird (Beta), Malix.
  • Various Delivery Agents– MPOP, MSwatch, Maildrop, Getmail, Procmail.

Suggested Read: 
How to Convert Maildir to Outlook

How to Import Maildir to Apple Mail?


There are hundreds of email client application having different types of storage format. Knowing all of them is next to impossible for a normal user. You might be not familiar with all of them but now you at least know what is Maildir file format. So I believe that this article might help you to update your technical dictionary. I hope you must have understood the inner workings and the whole structure of Maildir files.

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