deleting auto stored email addresses iPhone

How do I delete email addresses that were detected in prior emails and seem to be automatically stored on the iphone?

Specifically, these addresses are not in my contacts.

Annoyingly they "pop up" when I try to address and email - it's possible to inadvertantly send to the wrong recipient.

I've tried deleting the email account. Yet the data and the message are still stored somewhere.

Is there anything that can be done short of erasing all content and settings from the phone?

Is there any app to buy that will erase this data?