Just junk that's in there and they want to get rid of it because a lot of times they accidentally use that email address. It could even be spam or anything like that. It turns out these are email addresses of people that they received emails from. They see stuff in their Contacts, sure, but sometimes they see old email addresses, email addresses from people they don't know. People look at these suggestions and sometimes they see email addresses they don't even recognize. That's in the Mail app when you go to compose a new message, so let's do File, New Message, and you start typing the name of the person or their email address you get some suggestions.
Video Transcript: Here's what might be one of the most commonly asked questions of anybody that offers Mac help online. Check out Removing Unwanted Email Addresses in Mac Mail at YouTube for closed captioning and more options.
