I have been using the gmx.com email service with no problems whatsoever since I got my blackberry the day they came out. Today I (and my wife, and friend) have had the exact same problem that the storm2 keeps wanting me to validate the gmx account's email. I put it in and it "processes" for a bit, and then says the password is no good. I can go to gmx's website and login there with the same name/pwd and it works just fine.
Any ideas?
HSV06 friend here... I found that if you just remove the email account from your blackberry and set it back up using same password and such it would then work. Not sure what was up with that but seems to work fine after you do set it up again.