Spam relayed through backup mail server

[Choji]

Hi,

I have a problem that some spammers are sending mail to me through a third party, backup mail server.
This server doesn't have much of spam control and I have no way to configure it.
Any ideas for ways to improve the rules on spamassassin that runs on my own mail server to prevent these spams from getting through?

[scott]

You do the usual stuff already? (dcc, razor, dcc, etc)

[faris]

There's a spamassassin plugin that can add X to the score if it wasn't relayed through the primary MX. I could never get it to work properly, but that was 4 or 5 years ago. Might be worth looking for an update to that.

This third-party backup mailserver....I take it that it is listed as a mailserver in one of the domains hosted on your server's DNS records? Some spammers use the lowest priority (highest number) MX record, so you can add a third MX that's your server again to help prevent that, or add some blackhole MX records (some DNSBL providers offer such things as a way to catch spammers), or do both. This won't always work - I've noticed that some spammers try ALL MX records.

[Choji]

I didn't get around to configure Spamassassin for this, but I managed to filter these spams out before they got through the MTA using Spamdyke. I'd been using Spamdyke before but I realised some of the spam rules had been turned off. Re-enabling them seems to have done the trick.

Many thanks anyway!