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I have a setup of several frontend (MX) postfix servers using relay_domains. Some of the relay_domains are hosted on a postfix backend server that has the mailboxes. The other relay_domains are of customers running their own mailservers.

transport_maps is used to retrieve the nexthop destination (backend or customer server). Additionally, address verification is used to avoid accepting undeliverable mail - incoming mail is verified against either the backend or the customer server before accepting.

All information about domains/transports etc. is retrieved from a MySQL database, replicated from the backend to the MX frontends. That means, the frontends could actually use relay_recipient_maps to figure out for themselves, whether an address exists on the backend or not. The frontends would not have to bug the backend with verification probes. That is what I am aiming for.

However, the frontends do NOT know about valid recipients for the customers running their own mailservers. Hence, relay_recipient_maps cannot be used - as per postfix documentation, that would lead to all mail for those customers being rejected.

Is there a way to use relay_recipient_maps for backend domains while falling back to address verification for domains running their own mailserver?

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When the customers run their own mailservers, why should they use your relay server? They can send mails on their own. –  mailq Jul 3 '11 at 16:48
This question is about receiving mail, mailq, not sending it. –  JdeBP Jul 4 '11 at 12:43
Yes, this is about incoming mail. I'll explain anyways: those customers are mostly on DSL lines (considered dialup by some spam mechanisms / DNSBL). Also, the reverse DNS name doesn't match the server name (which cannot be changed since it's controlled by the ISP). Some MX give crappy spam scores to mail from such hosts (or even reject it completely). Basically, that's why. It also allows us to give better support for "They don't receive my mail! Why?" issues since we run only one centralized mail queue. –  riha Jul 14 '11 at 6:47
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