sendmail expects to the machine to have a FQDN (fully qualified domain name).

If it does not have that (type “hostname” to check what name the machine has) sendmail will complain about this and take a loot of extra time trying to find it.

To use a FQDN edit “/etc/hosts” and change [something] to [something.yourdomain.com] and this will go away. Updating “/etc/hostname” at the same time might be a good idea; don’t forget to run “/bin/hostname -F /etc/hostname” after updating /etc/hostname.