Nem tudom segít-e, de nálam ezek vannak:
local_destination_recipient_limit = 1
# ispCP Autoresponder parameters
ispcp-arpl_destination_recipient_limit = 1
dovecot-spamass_destination_recipient_limit = 1
virtual_transport = dovecot-spamass # -> a master.cf -ben is be van lőve a dovecot-spamass rész)