I was wondering how to troubleshoot this issue

Hi ,

Thank you for your question.

Could you tell me more details which is about message flow?

For example:

Did you send email to external? Or internal? 

Did internal message flow work without any problems?

Did MX record in ISP in destination email address? Is there NDR?

Did this issue occur when we send email to all domains or the specific domain?

We could telnet port 25 on Exchange 2013 from internal and external to check if port 25 was blocked. Then we could check firewall and anti-virus which was caused message flow problems and make sure we add the Exchange 2013 to firewall so it can use port 25 for outbound message flow.

Windows 2008 DNS behaves the same way as Windows 2003 DNS in this matter, we could refer to the following link to check if the issue persist:

https://support.microsoft.com/en-us/kb/828731/en-us

Then, we could check if there are any errors in application log.

If there are any questions regarding this issue, please be free to let me know.

Best Regard,

Hi ,

In addition to jim suggestions ,Just share us the last error message on the problematic queues by using the below mentioned command.

Get-Queue -Identity "mention the queue identity" | fl

Jim, this issue has been resolved - on e of the queues was filling up with internal messages since email address was not configured properly - I've opened up the queue and removed old messages and fixed email address on the service.  Thank you for your input