> Specific questions I had were if I can use the standard > DNS "load balancing" (multiple MX records, same priority, > possibly multiple IPs resolving to one A record) setup > *behind* a relay server (those MTAs behind the relay > only being available via the relay and never directly).
Well, it looks like I could do relay_domains = example.com transport table: example.com relay:other.com I have to use "other.com" in the transport because I need to use DNS-based "load balancing" of multiple SMTP servers on the backend, but the relay is listed as the primary MX for example.com (my understanding is that I can't do this: example.com relay:internal.smtp.example.com because mail would loop, right? So will using another (essentially junk) domain work for this? > Also need to make sure I know how address verification > works when ideally the relay doesn't have access to the > list of (virtual) users. It looks like with relay_recipient_maps empty, all mail just gets sent through the relay to the main SMTP server, which is fine. But when the main SMTP server gets mail to invalid recipients, how does it reject it? Am I correct to assume that because the relay server already did the SMTP conversation with the client, the main SMTP server can't do any real time address checks? This seems less than ideal. Also, it looks like any bounces or anything else that the main SMTP server needs to send back go through the relay if I specify it in either the "relayhost" setting or if I put it in the transport table with: * smtp:relay.example.com Is there a difference between that and relayhost? Which is better? Do both methods force postfix to send anything outgoing (bounces OR outgoing user email OR anything else) through that given host? > And assuming I can run postscreen on the relay and > not need to do much connection, client and RBL filtering > on the main MTAs (except address related since the > relay won't have access to local addresses). I still need to learn about this more, I don't know how much of my recipient/client/helo (etc.) restrictions I can put on the relay and how the main SMTP server will handle those restrictions that the relay can't handle when it is being relayed to indirectly.
