See MailboxFormat/dbox for a description of the dbox mailbox format. NOTE: You must not lose the dbox index files, they can't be regenerated without data loss.
dbox can be used in two ways:
One message per file (single-dbox), similar to Maildir.
Multiple messages per file (multi-dbox), but unlike mbox multiple files per mailbox.
To use single-dbox, use the tag sdbox in the mail location, for example:
# single-dbox mail_location = sdbox:~/dbox
For backwards compatibility, dbox is an alias to sdbox in the mail location.
To use multi-dbox, use the tag mdbox in the mail location, for example:
# multi-dbox mail_location = mdbox:~/mdbox
dbox has a feature for transparently moving message data to an Alternate storage area.
To specify an alternate storage area, use the ALT parameter in the mail location. For example, specifying the mail location as:
mail_location = mdbox:/var/vmail/%d/%n:ALT=/altstorage/vmail/%d/%n
will make Dovecot look for message data first under /var/vmail/%d/%n, and if it is not found there it will look under /altstorage/vmail/%d/%n instead.
Keep the unmounted /altstorage directory permissions such that Dovecot mail processes can't create directories under it (e.g. root:root 0755). This way if the alt storage isn't mounted for some reason, Dovecot won't think that all the messages in alt storage were deleted and lose their flags.
Mailbox directory name
When using the default hierarchical layout, there is a potential for naming collisions between dbox's dbox-Mails/ subdirectory and mail folders of the same name. For example, consider a mail folder "foo/bar". Under the default hierarchical layout, data about this mail folder would be stored at ~/mdbox/mailboxes/foo/bar/dbox-Mails/.
If the user then tried to create a mail folder "foo/bar/dbox-Mails", this would then imply that data would be stored at ~/mdbox/mailboxes/foo/bar/dbox-Mails/dbox-Mails/. But this would overlap the dbox-Mails/ subdirectory of mail folder "foo/bar".
This may not be a problem in many installations, but if a risk of collisions with the default name "dbox-Mails" is perceived, then the DIRNAME parameter can be used. For example, if we specify mail location as:
mail_location = mdbox:~/mdbox:DIRNAME=DbOx-mAiLs
then this will make data for mail folders be stored in a subdirectory DbOx-mAiLs/ instead of the default dbox-Mails/, so a mail folder "foo/bar" would have data stored at ~/mdbox/mailboxes/foo/bar/DbOx-mAiLs/.
The value for DIRNAME should be chosen carefully so as to minimise the chances of clashing with mail folder names. In the example here, unusual upper/lower casing has been used.