Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I'm new to TLS Authentication but have read and followed the following document with fine detail:

I have configured this in a virtual test environment and all appears to be working... mail flows... I can inspect the verbose email logs and I can see the certificate being sent and received within the log.

I am just not 100% sure that this means that TLS is working!

Does anyone know specifically with 100% certainty what fields in the message headers and/or the verbose logging which indicate that TLS is enabled and operational?

share|improve this question
up vote 1 down vote accepted
  1. When TLS is used to transmit a message to your Exchange server, the full "Received:" header (as visible when display of full headers is turned on in the receiving e-mail client) will include Microsoft SMTP Server (TLS) before the date.

  2. If you are in a "trust but verify" mood and want to know with 100% certainty, use a packet sniffer like Wireshark on either the sending or receiving server. Send a test message in your virtual environment; look for the port 25 SMTP traffic; if you see encrypted traffic after the SMTP session's STARTTLS command and there is no plaintext content, then TLS is working.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.