Looks like Dave sorted it.
Sounds like it was the automated email management thing. When your emails bounce back to the forum, your account gets locked down and a PM is sent with instructions on how to change your email address and get the account back in order.
We send hundreds of thousands of (mostly automated) emails each month across the whole network and its important for us to make sure we're not sending emails to email accounts that don't exist, as part of the terms and conditions of sending so many emails out.
All the ISP and email providers have different terms and conditions of sending so many emails but a lot of them get fussy about using their resources to bounce back emails that have been sent to accounts that don't exist.
So when your emails bounce back, your account gets automatically configured to stop all emails coming from the forum (in all forms, notifications about PM and threads etc too), and you get the PM showing you how to set the account back up.
Not 100% certain that's what it was but it sounds like it.