My customers are seeing this emailed to them. I assume it's because they are trying to reply to an email from the service desk system.
Any ideas where I need to look to stop this behaviour?

"Thank you for contacting the Service Desk.

To initiate a request you need to login to our Service Desk. You can login using your existing account information or create a new account right away. This system will ensure an accurate and timely resolution to any problem you may have. Please contact your System Administrator for more information."