Mailbox Formats
Mailbox formats supported by Dovecot:
mbox: Traditional UNIX mailbox format. Users' INBOX mboxes are commonly stored in /var/spool/mail or /var/mail directory. Single file contains multiple messages.
Maildir: One file contains one message. A reliable choice since files are never modified and all operations are atomic. The top-level Maildir directory contains the Maildir/cur, Maildir/new and Maildir/tmp subdirectories.
dbox: Dovecot's own high performance mailbox format. Mails are stored in one or more files, each containing one or more messages.
Cydir: Dovecot's own simple and high performance Cyrus-like mailbox format. It should be mostly used for testing and benchmarking only. v1.1+ only.
Mailbox formats not supported by Dovecot:
mbx: UW-IMAP's old high performance mailbox format. One file contains all the mailboxes, so expunges may still be slow.
mix: UW-IMAP's new (2006) high performance mailbox format. Similar to dbox.
mailstore: A format created by Exim.
MH: One file contains one message. Sort order of the folder determines the message ID and name. Actively used by projects such as MH-E, NMH, exmh. Experimentally supported by UW-IMAP.
MMDF: Similar to mbox, but instead of From-line separators it uses four ^A characters
Cyrus: One file contains one message, plus there are a couple of index/cache files. Commonly referred to as being maildir-like, although they have only a single thing in common.
Adding support for new formats for Dovecot isn't very difficult, although it can be time consuming. Dovecot exposes a nice and simple API which needs to be implemented.
Software Support
Format/Software |
|||||||||
Yes |
Yes |
No |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
|
No |
Yes |
No |
Yes |
No |
Yes |
No |
No |
No |
|
Yes |
No |
Yes |
Yes |
Yes |
No |
Yes |
Yes (3.22) |
Yes |
|
No |
No |
No |
Yes |
No |
No |
No |
No |
No |
|
Yes |
No |
No |
No |
No |
No |
No |
No |
No |
|
No |
Yes |
No |
No |
No |
Yes |
Yes |
Yes |
No |
Conversion Between Mailbox Formats
See Migration/MailFormat.
References
Mutt mailbox formats: http://rucus.ru.ac.za/docs/mutt/manual58.html
Article on mailbox formats: http://www.livejournal.com/users/rfunk/1571.html
Mbox and maildir comparison: http://www.linuxmail.info/mbox-maildir-mail-storage-formats/