How to add External SMTP on WHM/cPanel with GSuite Relay SMTP

Have you ever experienced emails from your server not reaching their destination — just disappearing? They've been sent without any errors, but the recipient never gets them. In this case, the issue is most likely in the email delivery process — it could be that the VPS where WHM is installed doesn't have port 25 open.

One of the most effective solutions to fix this is: Smarthost SMTP Relay. Here's how to set it up in WHM/cPanel:

1. Login to WHM as root / Administrator. Then go to the menu:
   Home >> Service Configuration >> Exim Configuration Manager.

2. Click on Advanced Editor.

3. In the Section: AUTH, add the following code

    excrelay_login:
    driver = plaintext
    public_name = LOGIN
    client_send = : USERNAME : PASSWORD
   

4. In the Section: ROUTERSTART, add the following code:

    send_via_excrelay:
    driver = manualroute
    domains = ! +local_domains
    transport = excrelay_smtp
    route_list = * smtp-relay.gmail.com
   

5. In the Section: TRANSPORTSTART, add the following code:

    excrelay_smtp:
    driver = smtp
    port = 587
    hosts = smtp-relay.gmail.com
    hosts_require_auth = smtp-relay.gmail.com
   

6. Click the Save button to apply the changes.