Sendmail configuration should be done in the /etc/mail/sendmail.mc file
To generate configuration changes, use the m4 macro processor:
<code> m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf </code>
To restart sendmail after making changes:
<code> /etc/init.d/sendmail restart </code>
Define the domainnames for which your mail server handles mail for in the /etc/mail/local-host-names file. For example, if you handle mail for example-abc.com, add this to the local-host-names file.
Restart sendmail after you make changes to this file.