A common request from my IT admin guys is how they deal with the failure of outbound emails. This will generally cause the phone to get hot very quickly and can also replicate to issues with the server itself. I always say try and keep an eye on queues as you can easily spot the problem, you can also use the monitoring tools within Exchange as well and get early warning but sometimes you’ll find they can issue false readings.
What we need to do is a bit of research; investigate into why mail queues are building.
There several bits of info you can gather to help you troubleshoot.
(NDR) Non Delivery Reports – These are very important as it will reveal the SMTP diagnostic code. If you have a user hassling you over the phone ask for the code then you can see the server error and find the problem.
Message Tracking Logs – Microsoft Exchange can track a message very well; it can tell you what it did with the message. This needs to be enabled, but run it all the time as the overhead is very low.SMTPDIAG Tool – SMTPDiag issues DNS queries using both UDP and TCP to validate the queries will succeed.
SMTP Logs – The logs that the SMTP server creates are not that good and may be limited but they can show if the connection was made. To enable RIGHT CLICK SMTP Virtual Server>PROPERTIES>GENERAL tab>PLACE a tick in ENABLE LOGGING