How to fix "unable to qualify my own domain name (myhost) -- using short name"?

Sendmail: short host name to FQDN via /etc/hosts entry

Reorder your /etc/hosts file entries:

127.0.0.1   localhost localhost.localdomain
127.0.1.1   myhost.mydomain.eu myhost.domain2.eu myhost

It should qualify myhost to myhost.mydomain.eu (the leftmost name in /etc/hosts line with myhost)