Mailbox Formats
Mailbox formats supported by Dovecot:
Name |
Tag |
Description |
|
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. |
||
sdbox |
single-dbox, one message per file |
Dovecot's own high performance mailbox format. Messages are stored in one or more files, each containing one or more messages. |
|
mdbox |
multi-dbox, multiple messages per file |
||
dbox |
deprecated alias for sdbox |
||
cydir |
Dovecot's own simple and high performance Cyrus-like mailbox format. It should be mostly used for testing and benchmarking only. |
||
imapc |
Use remote IMAP server as mail storage. |
||
pop3c |
Use remote POP3 server as mail storage. |
||
The Tag column indicates the tag which is used at the beginning of a mailbox location specification.
Mailbox formats not supported by Dovecot:
Name |
Description |
UW-IMAP's old high performance mailbox format. One file contains all the mailboxes, so expunges may still be slow. |
|
UW-IMAP's new (2006) high performance mailbox format. Similar to multi-dbox. |
|
A format created by Exim. |
|
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. |
|
Similar to mbox, but instead of From-line separators it uses four ^A characters |
|
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. Use Cydir format as an example.
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: https://rucus.ru.ac.za/docs/mutt/manual58.html
Article on mailbox formats: https://www.livejournal.com/users/rfunk/1571.html
Mbox and maildir comparison: https://www.linuxmail.info/mbox-maildir-mail-storage-formats/