Why is Sendmail not sending emails to Gmail?

Question

send mail

At the same time, mail arrives at Yandex
. In the logs
Apr 17 06:40:01 localhost sm-msp-queue[5575]: My unqualified host name (localhost) unknown; sleeping for retry
Apr 17 06:41:01 localhost sm-msp-queue[5575]: unable to qualify my own domain name (localhost) -- using short name
Apr 17 07:00:01 localhost sm-msp-queue[5612 ]: My unqualified host name (localhost) unknown; sleeping for retry
Apr 17 07:01:01 localhost sm-msp-queue[5612]: unable to qualify my own domain name (localhost) -- using short name

Answer 1

in /etc/hosts add
127.0.0.1 localhost.localdomain localhost hostname
127.0.1.1 hostname
hostname to your own which can be found from the console:
command: hostname

Answer 2

echo 127.0.0.1 my.cool.domain >>
replace /etc/hosts with your real domain. or change mta