I have a local postfix server, and i want it to only relay emails to the only local domain (localdomain.be): myhostname = localdomain.be mydomain = localdomain.be alias_maps = hash:/etc/aliases alias_database = hash:/etc/aliases myorigin = $myhostname mydestination = $myhostname relay_domains = $mydomain default_transport = smtp relayhost = mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 10.0.0.0/24 mailbox_size_limit = 64000000 message_size_limit = 1000000 recipient_delimiter = + inet_interfaces = all inet_protocols = all smtp_host_lookup = native This configuration works fine to allow relay mail locally and on external destination domains, but i would like it to be an impossibility to send to other domains (ie: gmail.com). relay_domains is supposed to ensure that but it does not seem to really filter since i can still send to my gmail address.