Yes, this is getting repetitive, but I'm going to post it anyway to keep track of 1and1's down time.
For the past few hours, their email service has been offline, which means you won't be able to send/receive mail. Maybe you'll be one of the lucky ones to receive, but you won't be able to send. Emails that you try to send may end up disappearing because their servers aren't working. You could try logging into their
webmail.1and1.com, but it may be bogged down from the flood of users. Don't even try to call because you won't get through. (I've tried.)
If it's any consolation, email their billing dept at
billing@1and1.com to respectfully complain and request a credit to your next billing cycle. They will give you a credit on your account.
Update 7/14/2010: You can check 1and1's server status at
http://status.1and1.com Thank you mortalwombat for the info.