(I have searched through pages and pages of previous threads before posting this)...

I've just changed the Paypal Website Payments Pro and Express details over to a new PP account. Nothing else.

When completing the checkout my customers are getting all the way through to the last level and then getting a white screen that reads:

"Email Error: SMTP Error: The following recipients failed: "

The order email gets received by me, without problem.
The confirmation email gets received by the customer, without problem.
The payment comes through to Paypal without problem, without problem.

Why isn't the checkout_success page appearing as it should do?

All the SMTP details are as correct (smtpauth etc.) and normal emails can be sent. In fact, nothing has changed in this respect from the previous, working, set-up.

Any ideas?????