Hi Mathew,
I'll certainly look at xp_smtpmail. I've not seen the website you mention either, so I'll have a peruse around there at some later point.
I've just spent a couple of minutes checking the permissions and I believe they're the same:
login corpdom\xtest has a role of sysadmin, and database access to XTest
This is the same as corpdom\rupertw
Database user corpdom\xtest has database role membership of public and db_owner
This is the same as corpdom\rupertw
Immediately after the xp_sendmail statement, @@error is 0, which makes me think it thinks it worked correctly.
Thanks for your suggestions. I don't really want to resort to an extra program because it'll mean more to remember when it comes to deployment, but I may have to resort to it.
Rgds