I manage a Microsoft network and we have an exchange server which has an issue I need help with. Here is the problem, up until about a week ago an individual from one of our customers was able to send us emails no problem. Now all of the sudden we can send them emails but they cannot reply or send them back. According to the user from the other company they receive no errors about the message being undeliverable. I can?t figure where the problem is because I had one of the users at the other company send an email to my personal account (an email account checked from the net) and I received it. I have made no changes to my exchange server which would lead me to believe it must be on the other companies end. Any thoughts or suggestions on how to go about further troubleshooting this issue?