How does “sendmail” send mails to any domain name?

Ashika Umanga Umagiliya asked:

I noticed that one of our servers (running Ubuntu) can send mails to any domain ( , using simple “sendmail” command.

But I cannot figure out how to configure similar setup in a new server. I cannot see any files such as “/etc/mail/” in the first server.

How does this work ? Does it use some other SMTP server to do actual mail delivery? Where can I find these settings?

My answer:

It’s probably running postfix, not sendmail. The sendmail command is provided mainly for cross-compatibility.

You’ll find the configuration files for postfix in /etc/postfix and documentation at the Postfix homepage.

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