unqualified host name unknown

Problem:

Sendmail takes forever to do anything (ie 60 seconds). Log messages like:

May 27 09:54:50 computer sendmail[28953]: My unqualified host name (computer) unknown; sleeping for retry
May 27 09:55:50 computer sendmail[28953]: unable to qualify my own domain name (computer) -- using short name

Solution:

I see users post this over and over - "sendmail hangs" or "sendmail takes forever to load"

The problem is that sendmail is looking for a FQDN, and it is probably finding your hostname before localhost and localhost.localdomain

your host file entry should have your simple hostname after the others:

/etc/hosts

127.0.0.1 localhost.localdomain localhost myhostname

If done this way, sendmail sees a FQDN for your loopback interface and will breeze right through.

(Source)