Previously, I wrote a tip about how to get rid of the pesky previous recipients on your Mac—those email addresses that you've typed in incorrectly or that you just don't want showing up as suggestions when you're composing messages. Turns out that there's a way to do that same thing in iOS 6, and I swear, the birds sing more sweetly and sunsets look more lovely when you know how to do it. And it's really easy, too. I know I say that a lot, but this time, I'm not lying.
So on your iOS 6 device, start composing an email, and then type the first few letters of an address you'd like to remove. As usual, you'll see the list of suggestions pop up.
If there's an address that you've previously sent to that does not appear in your Contacts list, it'll have a blue arrow next to it, as indicated above. Click the blue arrow, and you'll see a Remove From Recents button.
Oh, that's so awesome! Note, though, that if you want to remove an address that doesn't have a blue arrow next to it, you'll need to delete it from Contacts.
After you get rid of an address, Mail will no longer attempt to autofill it when you're composing an email. See, I told you I wasn't lying about it being easy! There's a first time for everything.