Hi Jason
Thanks for that, your reply helped me to find a solution. I've registered a separate domain and I'm going to move the site onto that so that I can then use an info@newdomain.com email address to send the emails from, then use the Reply-to solution you've suggested. In this way, we can allow our users to send emails via the system without it being too obvious to the recipient where they're coming from, and they can also then reply directly to our users.
Thanks again!