How to set up mail sending?

Question

System administration

What do I have.
There is a dedicated server on centos 6, to which the domain (dev.main.by) is attached for second-level development. It also has preinstalled and configured postfix.
The postfix config is default, except for three parameters:

myhostname = domaintwo.com
relayhost = 
mydestination =

The domaintwo.com domain is not bound to the server.
When sending messages through php, it gives the following log:

Jul 27 13:01:11 bitrix postfix/pickup[4721]: 9CD3E82D63: uid=600 from=<[email protected]>
Jul 27 13:01:11 bitrix postfix/cleanup[5106]: 9CD3E82D63: message-id=<[email protected]>
Jul 27 13:01:11 bitrix postfix/qmgr[3751]: 9CD3E82D63: from=<[email protected]>, size=908, nrcpt=1 (queue active)
Jul 27 13:01:11 bitrix postfix/smtp[5108]: 9CD3E82D63: to=<[email protected]>, relay=mail.domaintwo.com[93.252.2.4]:25, delay=0.11, delays=0.04/0.01/0.01/0.05, dsn=4.7.1, status=deferred (host mail.domaintwo.com[93.252.2.4] said: 450 4.7.1 Client host rejected: cannot find your hostname, [192.160.2.2] (in reply to RCPT TO command))

What could be the problem?

Answer 1

In smtpd_client_restrictions or smtpd_recipient_restrictions rules (depends on postfix settings).
If you are constantly sending mail from the IP address 192.160.2.2, add it to mynetworks.