Incoming emails - delay error

[smurfomatic]

I've been asked to look into an issue receiving emails from a certain domain (another school). We can send to them fine, but any messages sent to us get bounced back with:

Delivery is delayed to these recipients or groups:

joebloggs@ourschool.com

Subject: Blah

This message hasn't been delivered yet. Delivery will continue to be attempted.

The server will keep trying to deliver this message for the next 1 days, 19 hours and 55 minutes. You'll be notified if the message can't be delivered by that time.

Firstly - is this a problem at the sender's end, or ours? We are receiving external emails from other domains, and they can send fine to other domains except ours. A quick search seems to say it's a reverse DNS problem, though I can't see why this would be affecting only one sending domain. We have recently installed a second broadband line in parallel to the existing one (which still handles email traffic) - could this be causing the issue?

[Patrickv]

Hmm. What exchange server are you using?
Here are a few troubleshoots to help you?
1) Check your incoming filtering or blacklist.
2) Reboot exchange server.

That's what i can think of at the moment that might help

Regards,
Patrick

[smurfomatic]

Thanks Patrick. Forgot to post the solution on here - it was a reverse DNS lookup problem, solved by the IT technician at "the other end".