SELECT u.userid,
       999 AS uid, 
       8 AS gid, 
       rel_homedir(v.volume::text, u.userid::text) AS home, 
       ('maildir:storage='::text || u.quota::text) || ':ignore=Papierkorb'::text AS quota
FROM mailuser u, user_volume v
WHERE u.userid::text = v.userid::text;