I found error on my Mailbox server and can't find any description for this error:

Every 15 minutes I have a warning message EventId 1035 from MSExchangeFrontEndTransport.

Inbound authentication failed with error LogonDenied for Receive connector Client Frontend <ServerName>. The authentication mechanism is Login. The source IP address of the client who tried to authenticate to Microsoft Exchange is [127.0.0.1].

Any suggestion what it is can be?

• Edited by Kuzmin,Anton 19 hours 13 minutes ago

Have you installed any third-party products on your Exchange server that might be trying to send SMTP mail using TCP