Maildir File Format

All That There is to Know About: What is Maildir File?

Emails are saved in a database file saved locally on a Windows PC. These allow access to mailbox data even when not connected to the internet. It is the most common method of saving messages opted by many leading email clients. This post talks about one such file format and explains all that there is about what is Maildir file format. It provides a detailed introduction and what it is all about. This Maildir file extension contains all the relevant information about the topic. It is very useful for entrepreneurs and non-technical businessmen not familiar with the file type. In order to read such files , you can go for Maildir File Viewer to preview data with each sub-directory

Maildir File Extension

What is Maildir & Maildir ++ File : A Brief Introduction

It is an email format which is used for storing messages only. It is a more organized and systematic way of storing mailbox data. It was introduced by Qmail client and is used by many other applications like Mozilla Thunderbird. It creates a separate file with a unique name for each incoming message.

One Such Extension to Maildir was found, named as Maildir++ which aimed at supporting mail quotas & sub-folders. The Sub-directories within Maildir++ files start with (dot) "." (eg, " .Inbox ", ".Drafts " etc.). This Maildir++ files follows the same specification as that of Maildir

Maildir++ file Extension

Quick Glance at Maildir File Structure

After Knowing about What is Maildir. Lets know about Maildir Directory Structure. This file type organises each folder in a new directory. The most important ones are discussed below:

  • Tmp: It stores the emails temporarily for the current mailbox.
  • New: Each incoming message is saved in this sub-directory (which is unread). It saves the meta properties of emails including ‘Return-path’ and ‘Delivered-To’ details. This information can be crucial in forensic analysis and for tracing the route or path taken by the email. The Maildir file extension receives messages in RFC 822 format. It keeps the text integrity intact. This directory also keeps a record of creation date and any last modifications or edits made.
  • Cur: It saves all the messages that have already been read. This indicates the very organized structure of the Maildir file format. It creates a separate folder for keeping the opened messages. It helps investigators to examine a cybercrime by scanning only part of the database.
Mailfir file directory

The above image displays a pictorial representation of how a typical client stores data using Maildir file format. The structure defines a home directory that branches into a separate folder for each user. One can browse to different sub-directories created for each account to read emails corresponding to that particular mailbox.

Maildir File Naming Convention

This section will describe about basic file naming Convention of Mialdir file format.Generally, Maildir file is seen as a file as:

File Naming Notation : < basefilename > , < filesize >, < flag>,S=20238_2,S

Mac OS
File Name Description, S=20238_2, S Denotes Arrival Timestamp, S=20238_2, S Specifies the size of email message, S=20238_2, S ( or R , F) (Seen)S : Specifies that user has successfully viewed email message but not read them
(Read)R : Specifies taht user has successfully read email message
(Flagged)F : Specifies that user has flagged hat particular message

Benefits of Maildir File Format

Here are some of the advantages of using this Maildir Directory Structure in any emailing application:

  • It is a secure file format and has minimal chances of corruption or damage.
  • It can be used over a network file system without any kind of compatibility issues. It is easier to share and access across platforms or systems.
  • Maildir file extension has a great message filtration system. Incoming text is directly sent to appropriate subfolder.
  • It allows for faster access to emails because of its unique structure. It can be beneficial in forensic analysis of a data file and to detect a possible cybercrime.
  • It makes for faster searches, retrieval, deletion of emails from a Maildir file.

Maildir File Extension Compatibility

Here are some of the examples of where this file format is used:

  • Mail Servers: Qmail, Xmail, Exim, Dovecot, Courier Mail Server
  • Email Clients: Thunderbird(Beta), Pine, Malix, Mutt, Alpine, Balsa, Cone
  • Delivery Agents: Procmail, Maildrop, Getmail, MSwatch, MPOP


There are different email clients which have different storage types. All of which are difficult to understand and study. It can become difficult for a regular user to identify and repair a bug with their email client. They first need to understand the inner workings and database structure to solve any issue. This post discusses a well-known type and explains in detail about what is Maildir File Format. It provides a lot of useful information that can come in handy for any professional or IT student.