Save a draft in Mail on iPhone
In the Mail app , you can save a draft to finish later, or look at existing emails while you’re writing a new one.
Save a draft for later
If you’re writing an email and want to finish it later, tap Cancel, then tap Save Draft. To resume work on a saved draft email, touch and hold , then select a draft.
You can also swipe down on the title bar of an email you’re writing to save it for later. When you’re ready to return to your email, tap its title at the bottom of the screen.
With OS X 10.10 or later, you can also hand off unfinished emails with your Mac. See Use Handoff with iPhone.