Thinking about this, I might have been to specific in my question. At the fundamental level I would like to have 2 or more Postfix servers capable of receiving virtual mail for multiple domains, where one of the servers also handles relaying and local delivery. The rest should function as backup MX.
I've tried with relay_domains, but it matches on domain-level which is too much. I then applied relay_recipient_maps, but it don't seem to have any effect, which means that addresses is still matched on domain basis. Every Postfix will have access to a complete list of recipients through MySQL. So the question becomes two-part: Why can't I get relay_recipient_maps to work? How would you recommend to set up a backup MX? One obvious way is not to do it, but some of the mail is not mine, which is why I at least would like the option to run a backup MX.
