We're having issues with our mail server. Basically some emails from external networks are not being accepted by the mailserver.

After some debugging using telnet and looking through the logfiles, it seems that the issue has to do with encryption between the mailserver and the client. Emails that do not use SMTP encryption seem to go through but emails that do seem to fail.

More specifically, it seems that the connection is dropped after the client makes a "STARTTLS" request to the mailserver.

So I was wondering if anyone has any idea what could be causing this?


I later found out it was this hotfix (KB948963) that was installed a while ago:


Uninstalling it immediately solved the problem

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