I am unable to send email to another email address on my domain hosted on Plesk
This article applies to 123 Reg servers running Plesk.
This article will explain how you can turn off the local email hosting service for a subscription on your server using Plesk 11.
Please note: You will only be able to turn off the mail service for an entire subscription. If you wish to use this option on a per domain basis it is advised you create a subscription for each domain on your server.
Log in to your Parallels Plesk Panel.
Click on the Domains link on the left panel.
Click on the Open in Control Panel link for the relevant domain name.
Click on the Mail tab.
Click on the Change settings link.
Unselect the Activate mail service on domain option.
Click on the OK button to save the change.