HI Gus,
Thanks for the sugestion. I've tried using powershell on exchange to set the rights but I couldn't get this to work. As a quick fix I've created a domain account and made it a member of exchange admins and used this for the outgoing profile. This is working for now, and as we may be moving to Exchange 2013 in the summer, i'll wait until them to sort an account out with the appropiate rights.
Thanks,
Sherv