Symptoms
- Outlook cannot connect via TLS to a Plesk server after a Windows update (KB5018410).
- Outlook provides 0x800CCC80 or 0x800CCC1A errors.
Cause
KB5018410 breaks the ability to use secure SMTP. It also disables the TLSv1 and TLSv1.1 by default.
Resolution
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)
Add option -o tls_ssl_options=NO_TICKETinto the/etc/postfix/master.cfto disable the TLS Session Resumption functionality.
Workaround 2
Rollback the update KB5018410 on a client's PC.
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