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There are various file formats used to store email at various "stages" of the email generation, transport, storage process. This page is intended to provide information about them, concentrating on the ones most likely to be found (by me) in current use.

See AboutThesePages.


Introduction and ToDos

In addition to what I've found so far (some resources) and to learning some details about the file formats I need to deal with, I also want to note where the different file formats are used -- that is both by software package and by "spool" location -- perhaps a format is used in /var/mail/<username> but a different format is used by the MUA for individual user's mail files (or perhaps the formats of those files is something completely different, driven more by the designer of the MUA. (Why do I expect Outlook will have its own proprietary file format?)

File Formats Utilization

Some (most) of these are just guesses at this point (and presumably are based on the latest versions of the mentioned software):

Main User Mailspools (/var/mail/<username>)


  • Postfix
  • Qmail
  • Exim


  • sendmail


  • nobody?

Individual User Mail Files



  • Pine (in Mail or mail or ?)
  • Mutt (in Mail or mail or ?)
  • Elm (in Mail or mail or ?)


  • Outlook?

mh format

For now, I'm assuming this is somewhat old and possibly obsolete.

mbox format

From http://www.qmail.org/man/man5/mbox.html -- lots more good information there:

"An mbox is a single file containing zero or more mail messages."

I think mbox is a fairly common format, but I think maildir (see below) is the most modern and the coming thing, if not already the most common.

maildir format

From http://www.qmail.org/man/man5/maildir.html -- lots more good information there:

maildir is a structure for directories of incoming mail messages. It solves the reliability problems that plague mbox files and mh folders.

Note also that:

Mail readers supporting maildir use the MAILDIR environment variable as the name of the user's primary mail directory.

See also:


  • RandyKramer - 26 Feb 2002
  • <If you edit this page, add your name here, move this to the next line>

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Topic revision: r3 - 2004-10-07 - RandyKramer
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