How to send a letter from another server through your own iredmail SMTP?

Question

PHP

Hello. There is a main site site.ru on one hosting, there is its subdomain srv.site.ru - on another hosting (VPS).
Iredmail is installed and configured on the subdomain, port 25 is open, letters via roundcube are perfectly sent and received.

Question: How to send letters from site.ru through the mail server srv.site.ru?
Tried as smtp, function fsockopen srv.site.ru:25 produces "Connection timed out".

Answer 1

Try to do with site.ru

telnet srv.site.ru 25

If there is no connection, then look in the direction of the farwalls on both servers.
In general, the standard option is to put postfix on site.ru, for example, and configure relayhost on srv.site.ru there.
In this case, the mail system function will forward all messages through your mail server.