I have 3 email accounts on my iPad (WiFi, not 3G), gMail.com, cox.net, and plgassociates.com which is hosted by 1and1.com. I can receive email on all 3 accounts on the iPad and I can send email on the Gmail and cox accounts. I cannot send from the plgassociates.com account.
The settings are pop.1and1.com and smtp.1and1.com, SSL off, and I've tried ports 25, 110, 587. Nothing works. 1and1 tech support hasn't been much help.