How can I tell if I'm being used to relay spam?

[MianoVision]

I have a client that recently moved his domain to another server. His DNS zone is still on my box, as I have not deleted his account. He reports that he is still getting tons of spam on that account, but if DNS has propogated (It has everywhere we can tell) that should not be the case, right?

Is there a way to see if we are being used as a spam relay, and if so, can we stop it?

[sawbuck]

Why not just remove his zone file? One way to check for open relay: http://www.abuse.net/relay.html

[dezignguy]

He reports that he is still getting tons of spam on that account, but if DNS has propogated (It has everywhere we can tell) that should not be the case, right

Umm. I noticed that as well when I moved servers... it seems that spammers mostly use servers that have very stale dns data... so they'll still be using the mx record pointing to your old isp for a month or two after you've moved.

Why not just delete the account though... if it's been around a week, then there's likely no legitimate user that hasn't gotten the new dns data and switched over to the new server/account.