Sneaky Spammers...?

Spicer, Kevin Kevin.Spicer at BMRB.CO.UK
Sun Mar 2 16:47:25 GMT 2003

I don't know whether this is a new ploy, or just one I haven't noticed before as I've got rather better reporting in place now (and one of the mails in question landed in my inbox!)...

Like (I guess) many sites our primary MX is our border mailscanner (actually its also our secondary as its has addresses on two internet connections) and our ISP provides two fallback mailservers, which in the event of failure queue up mail and forward on to our MailScanner when it comes back up.  I've just noticed that some enterprising spammer seems to have decided its a good idea to send mail directly to these servers and let them forward on to our primary MX.  I'm fairly sure that this is what is happening, as a quick grep of our maillogs suggests that only spam is being recieved from the backup MX's (suggesting that the primary MX was in fact available throughout).

I noticed also that lists the two fallback servers as no.1 and no.3 on the list of 'blocked' IP's (fortunately I turned blocking off when I installed it).  This could have serious consequences for anyone who is using this, or other scripts, to block spam relays, as should their primary MX (MailScanner) - or its internet connection - go down the seconary MX would then accept mail which it would be prevented from delivering once the primary MX came back up! [David, this is why I've copied you on this, as I'm not sure if you're currently on the MS list]

It's debatable whether scripts that block based on IP's logged by MailScanner need to account for this or whether MS should refrain from logging the IP of hosts that are fallback MX's for the domain(s)(?)  I did notice that the MS spam log entry suggests that the IP of our fallback MX's belongs the the domain of the spammers (forged) address rather than reflecting its reverse DNS name - which is also misleading.

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