verdiğiniz linkte mail gönderimi için yapmanız gerekenler yazıyor zaten.

How do I setup the free relay on Postfix?

Using your favorite text editor simply

Open: /etc/postfix/main.cf
Add or Edit Line: relayhost = relay.redstationmail.co.uk
Run: service postfix restart

ve

How do I setup the free relay on CPanel

You must edit your settings in CPanel to avoid manual changes being changed by CPanel

In CPanel go to Main >> Service Configuration >> Exim Configuration Editor. Select Advanced Editor and find the textbox immediately below "Section: ROUTERSTART" then insert the following text into the textbox:

smarthost:
driver = manualroute
domains = ! +local_domains
transport = remote_smtp
route_data = "relay.redstationmail.co.uk"