Email addresses are valuable to users, and you don't want to mistakenly suggest you already know their email.
Unlike addresses, which are public, a users email is private. It is a privilege for a user to give it to us.
By using autocomplete it's noble to help save users work, but it can mistakenly give the impression that it is a record inside your database (or a public record, which is even scarier).
If a user is logging into your site regularly, they'll probably see their own email address as they type from the browser storage in the input field anyway. It's a function of the browser. But that's a record of information they themselves have previously entered.
Registration with an autocomplete could be alarming, as you have no previous relationship or permissions from them.