Starttls not showing on receive connector

grevels used Ask the Experts™
I have a few customers with exchange 2016.  They all have a 3rd party SSL certificate and it is designated for imap, pop, iis and smtp I have the main receive connector set to do TLS but for some reason when I connect externally to port 25 with a telnet program it connects but when I do ehlo it does not show 250-starttls.  I have port 25 and 443 open to the servers is there something else I need to do to the server for it to accept incoming tls or do I need to open more ports on the firewall?
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Sometimes it could;d be blocked at your network device may be firewall or how about internal?


Is it port 25 or should there be another port open for it
Its port 25 only but I roughly remember that there was CISCO device which can block these verbos.
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Michael B. SmithManaging Consultant

Lots of firewalls do not forward STARTTLS if they don't have the SSL certificate loaded on them. Cisco is one of them. Cisco ASA appliances implement something called "smtp inspection" that will prevent STARTTLS.

Generally you can look at the '220' header to determine whether you are talking to an Exchange server or to a firewall. Exchange looks like this:

220 Microsoft ESMTP MAIL Service ready

Followed by a datestamp. A firewall will look differently.

Generally speaking, the firewall should NAT or passthrough "without inspection" (unless you've configured it to do deep inspection in which case you wouldn't be asking this question). :-)
Pete LongTechnical Consultant

Mmm my money is on the Exchange receive connector? Did you enable TLS on there? I've never needed to open another port for a StartTLS connection, and I am the LordOfCiscoFirewalls?

When you said about that some loading the certificate on the firewall that made me realize our firewall does spam blocking when means that outside is talking to the firewall not directly to the email server.  which pointed me in the right direction that I have found the problem and have it fixed.  Thank you all for the thoughts on this.
Michael B. SmithManaging Consultant

Just FYI - you should award some points for assistance on our part. Thanks!

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