Had an issue late this afternoon where the queue "messages awaiting directory lookup" had over 5K messages in it. I wanted to point to the following documents which detail how to troubleshoot each queue:
Troubleshooting Mail Flow and SMTP
Exchange Transport and Routing Guide
Modifying Logging Settings for MSExchangeTransport
Exchange Transport and Routing Guide
Basically, Queue buildup in "messages awaiting directory lookup" is related to AD connectivity. Here's a couple of ways to test AD connectivity:
telnet dcname 389 / 3268 (dc / gc)
lpd dcname 389 / 3268 (dc / gc)
dcdiag dcname
It turns out that one of the sites only has a single domain controller, which was probably overwhelmed. Lesson: Exchange needs at least two domain controllers local to it's site. Connectivity re-established by itself, but the queue continued to grow. We tried restarting the SMTP service, but it was stuck in a stopping state. There's a couple options available for this situation:
1. Force the smtpsvc to stop:
sc stop smtpsvc /force
2. Issue an iisreset /restart command which will bring down all the services related to inetinfo.exe (including SMTP).
IIS Library
It's important to note that if IISreset cannot bring down inetinfo.exe gracefully, then it will force it to stop. This can be avoided by providing the /noforce switch.
Teo
