iterate_query in dovecot-sql.conf is missing
Problem:
doveadm force-resync -A INBOX doveadm(root): Error: User listing returned failure doveadm: Error: Failed to iterate through some users
Refering to http://wiki2.dovecot.org/AuthDatabase/SQL#User_iteration we need this in dovecot-sql.conf
iterate_query = SELECT email as user FROM mail_user