VPopMail

Dovecot supports authenticating against external VPopMail virtual domain manager. Dovecot must have been configured with --with-vpopmail to enable this. You can check this with dovecot --build-options. See also VMailMgr for another similar virtual domain manager.

If the vpopmail database contains plaintext passwords, it can be used for non-plaintext authentication as well.

passdb parameters:

cache_key: If set, you can use auth_cache with VPopMail. See PAM for more information about it.
webmail=IP: If IP address is specified, connections from it are assumed to come from webmail and VPopMail's webmail usage restrictions apply. (v1.2+)

userdb parameters:

cache_key: Like in passdb.
quota_template=TEMPLATE: Template to specify quota rule, %q in value expands to Maildir++ quota. (v1.1+)

Example

auth default {
  passdb vpopmail {
    args = webmail=127.0.0.1
  }
  userdb vpopmail {
    args = quota_template=quota_rule=*:backend=%q
  }
}

Using VPopMail's quota instead of Dovecot's

(FIXME: Doesn't quota_template described above solve this problem too?)

You can use VPopMail's quota limits (instead of Dovecot's limits) by configuring Maildir quota like:

plugin {
  quota = maildir
  quota_rule = ?:storage=0
}

"?" means that it uses an existing "maildirsize" file if it exists, otherwise quota is unlimited. VPopMail will recreate this file if it doesn't exist when delivering new mail with its quota setting.

VPopMail + MySQL

Alternatively, you can use the SQL backend with the following configuration:

driver = mysql
#
connect = host=/var/run/mysqld/mysqld.sock user=vpopmail password=YOURPASSWORDHERE dbname=vpopmail
#
default_pass_scheme = PLAIN
#
password_query = SELECT CONCAT(pw_name, '@', pw_domain) AS user, pw_clear_passwd AS password FROM vpopmail WHERE pw_name = '%n' AND pw_domain = '%d'
#
user_query = SELECT pw_dir as home, 64020 AS uid, 64020 AS gid FROM vpopmail WHERE pw_name = '%n' AND pw_domain = '%d'

Most vpopmail installations use 89 as the uid/gid, not 64020.