Some host providers block all email ports (like TCP/25 and TCP/587). Here’s simple of example of how to setup two STMP servers, where SMTP1 is a relay server (forwarder), and SMTP2 uses SMTP1 to send email. Both are using default configuration files with slight changes.
SMTP1 (smart host)
This config line allows SMTP2 to send email without SMTP authorization. For the sake of security it would make sense to restrict access to port 2525 using iptabes.
mynetworks = 127.0.0.1 <IP_of_SMTP2>
This goes to /etc/postfix/main.cf.
And the following
2525 inet n - n - - smtpd
goes to /etc/postfix/master.cf on SMTP1. So that Postfix opens TCP port 2525.
Add this to /etc/postfix/main.cf on SMTP2.
smtp_always_send_ehlo = yes<br />relayhost = 18.104.22.168:2527<br /><br />
After restart you should be able to send emails from SMTP2 via SMTP1‘s using port 2525.