Question : MX Record Issue

Hi I've got a customer that says that they can't email one of my email domains, they get a 550 #5.1.0 Address rejected error returned to them.  What's interesting is I am able to send test email from Gmail account and it comes through no problem.  When I do a tracert on the mail.mydomain.com it points to OpenDNS, but when I check my MX record it points to my mail server's IP.  Also in the error message that the customer gets the IP address identified as being associated with the email domain is completely wrong, not my server's IP and not even the OpenDNS IP returned by tracert.

Answer : MX Record Issue

I've seen the errors when someone is not receiving email from our servers due to improper SPF Records, but never the other way around where we could not get from them ...