Why did I get the sendmail message: "SMTP attack: command=NOOP, count=20"?

Solution In Progress - Updated -

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

Subscriber exclusive content

A Red Hat subscription provides unlimited access to our knowledgebase, tools, and much more.

Current Customers and Partners

Log in for full access

Log In

New to Red Hat?

Learn more about Red Hat subscriptions

Using a Red Hat product through a public cloud?

How to access this content