Emails are not DKIM-signed when sending with a smarthost

Symptoms

You may find that emails sent via smarthost are not DKIM-signed despite having a valid DKIM record.

Cause

This typically occurs when the smarthost is not configured to send emails with DKIM.

Resolution

1. Log in to the server via SSH or WHM's Terminal as the root user
2. Open /etc/exim.conf.local using your preferred command-line text editor

3. In your smarthost configuration, search for the following line:

   CONFIG_TEXT: transport = remote_smtp

4. Change this to the following:

   CONFIG_TEXT: transport = dkim_remote_smtp

5. Save and close the file

6. Run the following scripts to load the change:

   # /scripts/buildeximconf

   # /scripts/restartsrv_exim

Email should now be DKIM-signed when using the smarthost.

Additional Resources

How to edit a file on command-line