Fixing slow boot because of MTA (hostname)

/etc/hosts should be like this (replace yourhostname with the actual hostname of the computer)

127.0.0.1        localhost
127.0.1.1        yourhostname.example.com yourhostname
::1              ip6-localhost ip6-loopback
fe00::0          ip6-localnet
fe00::0          ip6-mcastprefix
fe02::1          ip6-allnodes
fe02::1          ip6-allrouters

Then "sudo dpkg-reconfigure exim4-config" in the simplest way possible