How best to activate new services

I’m looking for a good method to create and respond to service activation. For example, if a user registers on a non-Domino service (similar to eBay, yahoo, whatever), I will get back some email with a registration link. What I want to do, apart from activating the link, is to update my local Notes client to store some of the information I got in that email (username, password etc).

We can create the activation email in the external application in any way Notes needs it. For me, the best thing is to get an email with a button, but I don’t know if this is possible. Are there any other suggestions?