Elliot F wrote:
Another method (and a very scalable one) would be to store user data in DNS.
Ooh, don't suggest that sort of thing on a DNS admin list unless you really like having a cheese grater rubbed on all your private parts. That is a gross violation of the design of DNS (but of course I can think of an elegant way to do it with a tinydns instance ;-).
The queue/smtp-forward is a really good idea, but if I'm recieving the message, that means the primary MX (their server) is down. The domains aren't very large, so spammers haven't (so far) taken much notice of them (and haven't spammed me because I'm secondary.) If you're speaking from an infrastructure perspective, this is a pretty good idea, especially if you're doing routing for a heterogeneos pool of mail servers with no unified/consistent user information store.
Actually, once the spammers take notice of the domains, you will find that they will preferentially target the secondary MX records, on the (in this case correct) theory that they will be less strictly configured in terms of user validation. And you'll wind up being the source of spam blowback, since you will accept the message and be unable to relay it to the primary, hence you will have to bounce it.
John
