This article links to five in the appstore. They work by writing a message and then opening the email app and pasting the input into a new mail:

Wide Email
Lettera
Sideways
Touchtype
Compose

Firemail

If you’re jailbroken you can type SMS messages in landscape mode using biteSMS or iRealSMS from Cydia.

Robin

 razor@edgarbv.com  https://www.edgarbv.com