We have an exchange 2003 server and are using it as a relay for a webserver which sends out confirmation emails once a person completes a registration. Lately, we've been getting a lot of messages saying that the email to this recepient has been delayed and eventually it comes back as undeliverable. I can't seem to find any reason why this is happening. The queue on the mail server shows no pending emails. I have resolved the mx records of the receiving domain and am able to connect to their mail server over port 25 getting a 220 response.
I am a little lost on this. Can someone assist?