Outbound authentication failed with error KdcUnknownEncryptionType
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Gavin Ross
101
Reputation points
We have Exchange running in Hybrid mode, only using it for SMTP email. The issue we are having is that out of nowhere, Exchange will stop sending smtp emails and the error in the log is this. --
Outbound authentication failed with error KdcUnknownEncryptionType for Send connector Inbound Proxy Internal Send Connector. The authentication mechanism is ExchangeAuth. The target is SMTPSVC/smtpservername.
If I reboot the server, it will work for a few days and then I would get the same error again and smtp emails will stop. Does anyone have any suggestions on what could be causing this?
Domain Controllers are Server 2025
Exchange Server is 2019 CU14
Single Exchange Server running hybrid config. All Mailboxes are in Exchange Online.
Thanks,
Gavin
Exchange | Hybrid management
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