Feb 4, 2015 - Sendmail: unqualified hostname unknown; sleeping for retry unqualified hostname

Sendmail error logs

Feb  4 17:49:00 alpha-VirtualBox sendmail[11814]: My unqualified host name (alpha-VirtualBox) unknown; sleeping for retry
Feb  4 17:50:00 alpha-VirtualBox sendmail[11814]: unable to qualify my own domain name (alpha-VirtualBox) -- using short name

Solution

FROM:

127.0.0.1       localhost
127.0.1.1       alpha-VirtualBox

TO:

127.0.0.1       localhost.localdomain localhost alpha-VirtualBox
127.0.1.1       alpha-VirtualBox