How to establish SMTP relay from WordPress in Cpannel or Plesk server:
Create a email account from Cpannel or Plesk server.
Install Postman SMTP plugin at your WordPress website.
Enter Outgoing Mail Server (eg sg2plcpnl0004.prod.sin2.secureserver.net )
Enter outgoing server port: 465
Envelope from Email Address: firstname.lastname@example.org
Now test your contact form of WordPress website.
Now check the emails . All mails would be received to email id you have setup in contact form’s From field.