[Dovecot] users = virual + system (both with ldap backend) => Fatal: setgid(12(mail)) failed with euid=501(...

dear all

probably something trivial, just cannot get my way around it, my goal is to get sieve on local-system users too, so postfix hands lda over to dovecot errors with mail for system users:

lda(me): Fatal: setgid(12(mail)) failed with euid=501(me), gid=513(Domain Users), egid=513( Domain Users): Operation not permitted (This binary should probably be called with process group set to 12(mail) instead of 513(Doma in Users))

mail storage is in users' homes and these are on nfs3

which bits am I missing, please advise?

regards