After using Apple Mail for a few years you may have noticed that, when adding contacts to a new email message, a long list of email addresses appears. Some of these may be in your address book, but it’s often the case that these names are people you haven’t sent messages to in years or that you emailed once, but have no intention of emailing ever again.
Why the long memory? Apple’s Mail app, for the sake of convenience, collects the names of everyone you send email to so you don’t have to chase down an email addresses for people who aren’t in your Contacts app. It’s a nice feature, but may make addressing email messages a little messy after a few years go by. Fortunately, you have a couple of options for cleaning up the mess.
Read more here:: Goodbye to the ghosts of emails past