smtp relay security to allow only certain domains
On the smtp relay-control there could be a domain list, which domains can relay mail. This would force the "from" field of the mail to come out of this list of domains. I could add mycompany.com and my2ndcompany.com to this list so users cannot use a different from-adres. This would add security if someones username/password got stolen without them knowing and authenticated smtp-relay is allowed.