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+Domain (%d) is empty
+====================
+
+IMAP or POP3 protocol doesn't have explicit support for domains. The usernames
+are commonly in user@domain format, and that is also where Dovecot gets the
+domain from. If the username doesn't have @domain, then the domain is also
+usually empty (unless 'auth_default_realm' setting is used).
+
+If you login as user@domain, but the %d is still empty, the problem is that
+your configuration lost the domain part by changing the username. Dovecot
+doesn't keep track of the domain separately from username, so if something
+changes username from "user@domain" to just plain "user", the domain is lost
+and %d returns nothing. If you have 'auth_debug=yes', this shows up in logs
+like:
+
+---%<-------------------------------------------------------------------------
+Info: auth(user@domain.org): username changed user@domain.org -> user
+---%<-------------------------------------------------------------------------
+
+Below are some of the most common reasons for this.
+
+Settings
+--------
+
+'auth_username_format = %Ln' lowercases the username but also drops the domain.
+Use 'auth_username_format = %Lu' instead.
+
+'auth_username_format' changes the username permanently, currently it's not
+possible to make it affect only the authentication part.
+
+SQL
+---
+
+'password_query' gets often misconfigured to drop the domain if username and
+domain are stored separately. For example:
+
+---%<-------------------------------------------------------------------------
+# BROKEN:
+password_query = SELECT username AS user, password FROM users WHERE username =
+'%n' AND domain = '%d'
+---%<-------------------------------------------------------------------------
+
+The "username AS user" changes the username permanently and the domain is
+dropped. You can instead use:
+
+---%<-------------------------------------------------------------------------
+# MySQL:
+password_query = SELECT concat(username, '@', domain) AS user, password FROM
+users WHERE username = '%n' AND domain = '%d'
+---%<-------------------------------------------------------------------------
+
+Or you can return username and domain fields separately and Dovecot will merge
+them into a single user field:
+
+---%<-------------------------------------------------------------------------
+password_query = SELECT username, domain, password FROM users WHERE username =
+'%n' AND domain = '%d'
+---%<-------------------------------------------------------------------------
+
+(This file was created from the wiki on 2019-06-19 12:42)