Bogdan Motoc - CRC wrote:

The main reason for setting up this secondary MX is to have a place for mail to go to when the mailserver that's supposed to receive them is down. It works, but there is a downside: my email server is leaking a lot of junk email, because it is being used to spread spam by sending mails to inexistent users on those domains with valid return addresses. The primary MX refuses the messages, and so they get bounced; exactly what the spammers intended in the first place. And this gets my mail server blacklisted, thus hurting all my users.

The questions are:
1. what are the options for checking if the user is valid and has not reached it's quota for a setup like mine?
2. how can I stop sending back the emails that the primary MX rejects?

Simply use a SPAM cotrol enabled version of Qmail, i.e., qmail-spamcontrol. It will do everything you asked, and more. It's really just qmail with a hole bunch of spam related stuff added. It can reject emails (and not send a bounce) long before it ever gets to your spam filter, by checking if the user even exists on your system first. Read the doc and features at:



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