How to send emails via POSTFIX+DOVERCOT?

Question

Nginx

Who fumbles help to understand the topic. I am making a mail server on postfix + mysql + dovecot + tls + nginx + postfixadmin + roundcube on Centos 7. I set everything up and it turns out to connect only via pop3 / imap to the incoming mail server (although incoming mail does not arrive in the mailbox), and smtp does not work, in the mail client indicates an error 504 5.5.2 - Helo command rejected: need fully-qualified hostname.
In RoundCube, after installation, there are test forms, again, IMAP is tested for OK, and SMTP waits a very long time and then gives an An error occurred error, although the letter is sent.
Where to look? Where to look for the reason?

Answer 1

and smtp does not work
Helo command rejected: need fully-qualified hostname.
well, here's the problem, see the config or post the postfix config here
and give the link for which article you configured

Answer 2

Eshkin cat, the error is written in English and white - need full-qualified hostname, that is, a fully qualified host name.