- Outlook cannot connect via TLS to a Plesk server after a Windows update (KB5018410).
- Outlook provides 0x800CCC80 or 0x800CCC1A errors.
KB5018410 breaks the ability to use secure SMTP. It also disables the TLSv1 and TLSv1.1 by default.
Install one of the following updates on the client PC, accordingly to the OS version:
- Windows 11, version 21H2: KB5018496
- Windows 10, version 20H2; Windows 10, version 21H1; Windows 10, version 22H1; Windows 10 Enterprise LTSC 2021: KB5020435
- Windows Server 2022: KB5020436
- Windows 10 Enterprise LTSC 2019; Windows Server 2019: KB5020438
- Windows 8.1; Windows Server 2012 R2: KB5020447
- Windows Server 2012: KB5020449
Note: If the update is not available via Windows Update Center, download and install it directly from the Microsoft Update catalog.
Alternatively, one of the following workarounds can be applied:
Workaround 1 (Plesk for Linux)
-o tls_ssl_options=NO_TICKETinto the
/etc/postfix/master.cfto disable the TLS Session Resumption functionality.
Rollback the update KB5018410 on a client's PC.
This is proving to be an absolute nightmare. My email has stopped working which is hosted by Plesk and I cannot setup a new one on Outlook on my new PC either? When will this be resolved? The work arounds don't work and I can't find that update either?
Hello Paul O'Halloran,
The issue described in this article has already been fixed on the Microsoft side. If you still having issues after the corresponding KB update was installed, it is most likely a separate issue. I suggest you to reproduce it and check /var/log/maillog for error messages.
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