Configure Smarthost eMail Relay in cPanel

Issue: Server 1 (abc.domain.com – xxx.xxx.xxx.xxx), is powered by cPanel, running Exim. Server abc.server.com is unable to deliver email to some recipients, as it is an innocent victim of collateral damage caused by an RBL unilaterally blocklisting an excessively large number of network IP ranges.

Solution: Configure abc.domain.com to relay all email to server 2 (xyz.domain.com). This is commonly referred to as a “Smarthost”. To facilitate the solution, follow the steps below.

On the server 2 (xyz.domain.com) that will receive the email (from server 1 to ultimately relay email to recipients)…

Log into cPanel (of server 2), and navigate to:

Home >> Service Configuration >> Exim Configuration Manager >> Access Lists
(the “Access Lists” tab).

Edit the setting for “Trusted SMTP IP addresses” and add the IP address of server 1 (xxx.xxx.xxx.xxx).
Also edit the setting for “Backup MX hosts” and add the domain name for server 1 (abc.domain.com).

Save the changes to restart Exim.

On the server 1 (abc.domain.com) that will relay the email (to server 2):

Log into cPanel, and navigate to:

Home >> Service Configuration >> Exim Configuration Manager >> Mail
(the “Mail” tab).

Edit the setting for “Smarthost Support” to reflect the details for server 2. The syntax is:

* xyz.domain.com

Note: There is a space between the wildcard (*) and the FQDN.

Save the changes to restart Exim.

Server 1 (abc.domain.com – xxx.xxx.xxx.xxx) will now relay email to server 2 (xyz.domain.com). Server 2 will send email to recipient email addresses.

Once the RBL has corrected the excessive blocking, the above configuration should be removed from both servers, and Exim restarted on both servers.

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