Send a test email

mail -s "test" user@example.org < /etc/redhat-release

Or:

echo `date` | mailx -v -s "Test - `date`" user@example.org

Verify the ability to send mail (doesn’t send anything)

sudo sendmail -bv user@example.org
sudo sendmail -bv localuser

Verify the ability to send mail using a custom sendmail.cf

sendmail -C sendmail.cf -bv user@example.org

sendmail.mc

This is the main Sendmail configuration file. It is compiled to sendmail.cf using this command:

m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

sendmail.cf

This is the compiled Sendmail configuration file. See sendmail.mc for generating this file.