Unable to qualify my own domain name
In order to fix this problem, you will need to specify a domain name in /etc/hosts file in the next format:
#/etc/hosts #[ipaddress] [longname] [shortname] 127.0.0.1 htmlviewer.net htmlviewer
If you don't have a registered domain, you can set any domain name as longname:
127.0.0.1 localhost.localdomain htmlviewer
It doesn't matter what you will set as domain name as long as the domain name is specified in valid format.
Finaly, restart sendmail to reload the new configuration of hosts file.
#service sendmail restart