Hi,

I dont' know where the field "username" should come from because I don't use this field (or query).

perhabs this is the problem? ;-)

The relevant files are:

Output of "dovecot -n" would be better, together with the additional files.

dovecot-sql.conf.ext

password_query = SELECT userid AS user, password,
home AS userdb_home, uid AS userdb_uid, gid AS userdb_gid,
concat('*:bytes=', quota_bytes) as userdb_quota_rule
FROM users WHERE userid = '%u'

I think you're missing a user_query.

best regards,

Anton