Hi,

Exchange Transport service failed to start after installation of a transport agent signed using self-signed certificate. Is it not possible to sign a transport agent with self-signed certificate?

Can you please tell what kind of transport agent is it ?

Is it an agent for any email signature , Antispam , Antivirus ?

Try checking your event logs to check for related errors.

Also check in what  account the Transport service is running.

More info on the transport agent will help in further troubleshooting

It is a custom routing agent that simply checks the subject of the email. It works perfectly fine without signing the DLL binary. However, after we signed the DLL binary file with a self sign certificate, Exchange Transport service failed to start.

As Sathish pointed out the first place to start is look at the event log, if the Transport Service fails to start you will have an error that should be pretty specific as to what the problem actually is. I suspect your getting "strong name validation" error but the log will tell you exactly what the issue is.

Cheers
Glen