If you mean email templates there are these 2 RFEs:
Bug 8026 - Email templates &
Bug 14426 - Save e-mail as template option
A trick people used to do was use the right-click > edit option to make a template, this will be back in 5.0.9:
Bug 28717 - Edit Missing from Right-click Context Menu for Message
If you meant in 'letter paper format size' like something in an office document, you don't do that with email. You could create a HTML email that looks 'letter-esk' I suppose. Zimbra currently uses a text or rich text editor, there is this RFE:
Bug 16386 - Raw HTML Source Editor in Mail Compose