Sorry but there's not much I can diagnose about this issue -- nobody else has reported this issue (and I haven't had it happen to me) so I think it is an issue somewhere else in the chain (like it not getting sent by the outgoing mail server or getting marked as spam somewhere before even getting to you?).

What happens if you sign up with the same admin email address that you know is working? And/or try it with a non-hotmail account (even could use something like mailinator.com for temporary one-off addresses)?

It works fine with the admin account (gmail) and the temporary Mailinator account. Weird - must just be something to do with hotmail... Never mind, I'll look into it and if I can't get it to work it's not massively urgent anyway. I assume it's a one-off or something I did because I'm sure other people would have noticed if it didn't work with hotmail!

By the way, I just want to say thanks for all your contributions to this community - I just started using Concrete5 a few months ago and have found some of your plugins invaluable. Plus it seems whenever I have a question or a problem I google it and you are the one who's answered!

Email problems are notoriously tricky to solve because there are so many steps in the process of getting from point A to point B -- many of which are not under our control as developers.

Good luck figuring it out, and thanks for the positive feedback -- I'm glad I could be of help! You might be interested in my Concrete5 blog (once- or twice-weekly tips for designers/developers who build C5 sites):http://concrete5tricks.com