Why did I get the sendmail message: "SMTP attack: command=NOOP, count=20"?
Issue
I got the following NOOP message in sendmail.
Nov 9 10:01:37 rhel73 sendmail[15974]: 1A90xlpf015974: localhost [127.0.0.1]: possible SMTP attack: command=NOOP, count=20
What does this mean?
How should I do for this message?
Environment
Red Hat Enterprise Linux 8
Red Hat Enterprise Linux 7
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