Where does autofill come from for iPhone mail app?

Fresh new phone- not restored from iCloud- when I set my email account up in the "Mail App" it pulls the autofill database from iCloud somewhere. There is an option to delete email addresses from this "Autofill" but its only done 1 at a time. Is there a way to delete the batch? All of them completely?

I tried a couple of apps that can browse the phone (iexplore for example) but they do *not show any recent email addresses due to the fact the phone is brand new. (guessing here but it checks a local cache vs whatever mail.app uses from iCloud??)

This neat phenomena is repeatable across several new devices. Its definitely something stored in iCloud thats populated when the phone is setup (even without an iCloud backup restore when you take the new phone out of the box)

Anyone figured out how to wipe something like this?