7,925 questions
What version of TLS is enforced on the 2016 server? Hopefully 1.2 and that the sending server that is failing supports that.
Exchange 2016 receive connector drops connections
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Евгений Котляревский
41
Reputation points
Hi there!
Exchange 2016.
I've created receive connector (FrontEnd, port: 12825) with "Require TLS" option enabled. TLS-certificate is configured and it's trusted by clients
While testing I've encountered weird behavior.
Some applications was able succesfully connect to this connector and succesfully send a messages.
But one of application - can't. In SMTP receive logs I see "235 2.7.0 Authentication successful", but then "Remote(SocketError)".
Here is the SMTP-receive log fragment with error (from "Bad application")
And here is log with successfully messages sent (from "Good application")
It seems pretty equal, except last string.
What can cause such behavior?
Exchange | Exchange Server | Management
1 answer
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Andy David - MVP 157.8K Reputation points2025-05-29T21:41:23.71+00:00 -
Евгений Котляревский 41 Reputation points
2025-05-30T06:02:46.7866667+00:00 I bleive both client (Windows Server 2022 Standard) and exchange support TLS 1.2.
And WireShark says they are (if I interpret the result correctly):And exchange SMTP-receive log says TLS 1.2 is used:
If it not enough, please tell me how to check this to be sure
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Евгений Котляревский 41 Reputation points
2025-05-30T14:37:23.6266667+00:00 Some Updates:
Continuing to investigate the issue, I created a test send connector without TLS with authentication only, and targeted my application to it. But the test still continued to report an error and the SMTP-receive logs still showed the message "Remote(SocketError)". But with such a connector I was able to look into the logs (because the traffic became unencrypted) and I saw "mail from:" command, "rcpt to", and finally "quit". So test in fact complete successfully. Also I saw, application during the test sends message to the same mailbox it try to sends from.
So I loged on in that mailbox - all test messages was there. This is not exchange case, it is problem of the application.
But few quiestions still persist:- why the SMTP-receive logs don't show the commands "mail from", "rcpt to" and so on when we do authenticated sending (without TLS)? When I try to do anonymous sending on the other connector, smtp receive log shows all of these commands.
Here how anonymous sending looks for example:
- Why I see "Remote(SocketError)" in SMTP-receive logs while authenticated sending?
- why the SMTP-receive logs don't show the commands "mail from", "rcpt to" and so on when we do authenticated sending (without TLS)? When I try to do anonymous sending on the other connector, smtp receive log shows all of these commands.
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