mailu/core/postfix/conf/sqlite-virtual_alias_maps.cf

dbpath = /data/main.db
query =
  SELECT destination
   FROM
     (SELECT destination, email, wildcard, localpart, localpart||'@'||alternative.name AS alt_email FROM alias LEFT JOIN alternative ON alias.domain_name = alternative.domain_name
      UNION
      SELECT (CASE WHEN forward_enabled=1 THEN (CASE WHEN forward_keep=1 THEN email||',' ELSE '' END)||forward_destination ELSE email END) AS destination, email, 0 as wildcard, localpart, localpart||'@'||alternative.name as alt_email FROM user LEFT JOIN alternative ON user.domain_name = alternative.domain_name
      UNION
      SELECT '@'||domain_name as destination, '@'||name as email, 0 as wildcard, '' as localpart, NULL AS alt_email FROM alternative)
   WHERE
     (
      wildcard = 0
      AND
      (email = '%s' OR alt_email = '%s')
     ) OR (
      wildcard = 1
      AND
      '%s' LIKE email
     )
   ORDER BY
     wildcard ASC,
     length(localpart) DESC
   LIMIT 1