iredmail-doc/en_US/howto/change.mailbox.format.md

Change per-user mailbox format (e.g. maildir, mdbox)

iRedMail uses maildir mailbox format by default, it's easy to backup, migrate and recover. As long as mailbox grows larger and larger, the performance will be slower due to too much disk I/O - caused by maildir format. Dovecot's own mailbox format mdbox has very good performance for large mailbox due to reduced disk I/O.

You may want to switch to other mailbox format for some reason. To help you switch easily, iRedMail-0.9.9 introduces 2 new SQL columns (for SQL backends) and LDAP attributes (for LDAP backends) to help you switch per-user mailbox format easily. All mailbox formats supported by Dovecot are supported in iRedMail.

!!! attention

* If you're running an iRedMail release earlier than iRedMail-0.9.9, you can
  upgrade it by following [iRedMail upgrade tutorials](./iredmail.releases.html).
* iRedAdmin-Pro RESTful API interface supports changing mailbox format too.
  Check its [API document](./iredadmin-pro.restful.api.html) (expand all
  parameters and search `mailboxformat` or `mailboxFormat`).

!!! warning

With `mdbox` format, if mailbox index files are damaged or lost, mail
messages will be lost. Because one of the main reasons for dbox's high
performance is that it uses Dovecot's index files as the only storage for
message flags and keywords, so the indexes don't have to be "synchronized".
Dovecot trusts that they're always up-to-date (unless it sees that
something is clearly broken).

Please read documents on Dovecot website to make sure you fully understand
the pros and (most importantly) cons of the format you're going to use:
[Mailbox Formats](https://wiki.dovecot.org/MailboxFormat).

!!! warning

- Changing mailbox format does not migrate existing mailbox for you. You
  have to migrate it __BEFORE__ switching to new mailbox format, then
  update SQL/LDAP data to use new mailbox format right after migrated the
  mailbox.
- New mailbox format will be used by Dovecot immediately after SQL/LDAP change.

SQL backends

You can switch to different mailbox format with SQL commands below. We use MySQL for example here.

USE vmail;
UPDATE mailbox SET mailboxformat='mdbox', mailboxfolder='mdbox' where username="user@your-domain.com";

• Value of mailboxfolder can be any folder name supported by Linux/BSD file system, but value of mailboxformat must be one of the formats supported by Dovecot, e.g. maildir, sdbox, mdbox.
• Value of mailboxfolder can not be same as previously used one, otherwise old mailbox will be messed up when Dovecot delivers new email.

LDAP backends

You need some LDAP management tool like phpLDAPadmin, Apache Directory Studio, or command line tool ldapvi (you can install it with yum or apt-get command directly) to update mail user's LDIF data.

mailboxFormat: mdbox
mailboxFolder: mdbox

• Value of mailboxFolder can be any folder name supported by Linux/BSD file system, but value of mailboxFormat must be one of the formats supported by Dovecot, e.g. maildir, sdbox, mdbox.
• Value of mailboxfolder can not be same as previously used one, otherwise old mailbox will be messed up when Dovecot delivers new email.
• With iRedMail-0.9.9, if attribute mailboxFormat and mailboxFolder don't present in user LDAP object, Dovecot is configured to use maildir as default mailbox format and Maildir (case-sensitive) as folder name.

Reference

• Doveadm Sync. It mentions how to easily migrate existing mailbox to new mailbox format with doveadm sync command.