So, I see that Virtual can auto load a remote Webmin server with new virtual server domains so that the remote can function as a backup store and forward email server. That’s great, except…
Assuming one is using postfix to deny invalid users, I don’t see where there is any sort of list on the remote of valid recipients. This means, the remote would accept all sorts of invalid users, and, when the primary came back up, bounce them.
This isn’t good, or, did I miss something? I’d prefer the backup server not accept invalid users.
This is true, but I don’t think Postfix would bounce them…I think it would trash them, by default. But I might be wrong about that. I’ve never used Postfix in this way. Hopefully you wouldn’t be offline for long enough to collect up a large number of invalid messages anyway, though, right?
Also, is there a way to make Postfix aware of valid users without actually being able to deliver for them? If there were, Virtualmin could add that data as well–it’d be trivial to add that, but I don’t know of any way to do it. We just implemented an example we found in the Postfix docs a couple of years ago. If there’s a better way to do it, we’d be happy to hear it.
I am sure there is, I will experiment and submit enhancement once done.
Here’s the other part of this - it’s not just with down systems. Many spammers attack secondary MX servers and beyond when they are denied from the main server. So, what happens is a lot of time, the primary denies them, the secondary accepts them. Which causes more trouble than it is worth. Sometimes, it’s a backdoor way to get SPAM in.
Even though Postfix might delete them, it’s a lot of unnecessary traffic and work.