Alright here goes...I have an Exchange 2007 server working as our e-mail server here. The problem is that usually it will send and receive both internal and external mail without issue - however periodically, it will stop receiving external e-mail altogether yet still be able to send both internally and externally as well as receive internally.Can someone please direct me on where to start with troubleshooting this?

Are there any events in the application log indicating a problem? If youre not able to reproduce the issue, next time it happens look at the queues and see if messages are being backed up and document why. Also attempt to test connectivity to port 25 on the server from the internet and document your results.How to Use Telnet to Test SMTP Communicationhttp://technet.microsoft.com/en-us/library/bb123686.aspx Mike Crowley A+, Network+, Security+, MCT, MCSE, MCTS, MCITP: Enterprise Administrator / Messaging Administrator

Hi, I think that you firstly need to know where the issue occurs. Whether the issue occurs when external mail server attempts to telnet to your Exchange server to submit the message or the issue occurs when your Exchange Server process the messages after receiving the message. The NDR message is helpful to check the issue. If the issue occurs when external mail server attempts to telnet to your Exchange server to submit the message, the remote mail server is responsible for generating the NDR message. If the issue occurs when your Exchange Server process the messages after receiving it, your Exchange is responsible for generating the NDR message. Therefore, you should be able to check the message header of the NDR message in order to know who generates the message. If the issue occurs when external mail server attempts to telnet to your Exchange server to submit the message, you can enable SMTP log to check the issue. You can also check the MX record by using NSlookup tool. You can also manually telnet to your Exchange Server from external client to test the issue by referring to the article provided by Mike Crowley. If the issue occurs when our Exchange Server process the messages after receiving the message, you can use Message Tracking Log, Queue Viewer and Event Log to help troubleshooting the issue. Mike