Draft: domains: seperate into domains and relayDomains

Marcelrequested to merge
SuperSandro2000/nixos-mailserver:relay into master

Add support for configuring mail server for domains where users should not be able to receive/send mails. This is useful for using this mail server also as a relay, e.g. for hosting a mailman.

Closes !333 (closed)

Also restrict LDAP users from sending from relay domains.

Edited by Marcel

Merge request reports