This Error Event is part of Send Email Events.
Event ID · 50451
"NTLM authentication failed"
Overview
The error indicates that Send Email Action has failed to authenticate during communication session with SMTP server.
Cause
Possible cause is that specified SMTP server does not support NTLM (NT LAN Manager) or incorrect username or password is specified.
Solution
Try removing username and password, if specified, since logging into domain should be sufficient to send an email.
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