domain name problem

Oct 8 05:01:50 servername sendmail[400]: My unqualified host name (servername) unknown; sleeping for retry
Oct 8 05:02:50 servername sendmail[399]: unable to qualify my own domain name (servername) -- using short name

hi, dmesg catch this error. so what is it about and what shall i rectify about it?

Fully qualify your hostname in /etc/hosts. Add an alias thus:

[hostname].

The "." at the end of the hostname will fully qualify it.