I'm running Mail 3 on Leopard, and all my accounts are IMAP, I just found something that surprised me (it could well have been there all the while).
When I had the following in my clipboard:
...and paste whilst looking at an inbox in Mail, it created a new unread email with the contents as:
MY EVENTAttend ffconf.org 2018
The UK's best JS and web development conference. 8 amazing speakers, workshops, socials — find out more & get tickets today.
From: [email protected] Subject: You're hired Dear thingy, We liked your mad skillz so much, we're going to throw money at you.
And paste it in to Mail, you'll find a new email.
Might be fun for a practical joke at some point...