I haven't seen this fix mentioned in any of the forums I've read over the last two weeks but if you have a problem with your Blackberry not recieving Emails try this as a fix - it worked for me and it took me a while to find it!

I just went into my Email Account Settings on the PC, clicked on "More
Settings" and then on "Outgoing Server". I then checked the box marked "Log Onto Incoming Server Before Sending Mail."

My 8900 is now back doing what it's supposed to do - no thanks to my ISP Helpline, The Blackberry Website or any number of well intentioned forums. Give it a go!

Like any fix, it really depends on your setup (there are a number of different ways to get email from different types of email accounts) and the actual cause of the email interruption.