However, people change email addresses. There’s a way to delete old or unwanted addresses from the Auto-Complete list in Mail. The Mail application remembers all new addresses automatically, and soon the auto-complete feature is useful again.

Delete a Recurring Email Address Using the Auto-Complete List

When you want to remove auto-complete addresses, you can do it by working directly in the Previous Recipients list. To remove an email address from the auto-complete list in Mac OS X Mail or macOS Mail: If you want to remove all the listings for a person with more than one email address, click in the search results field, use the keyboard shortcut Command+A to select all the results, and then click Remove From List.  Select the search field and start typing the name or email address of the person you want to remove from the Previous Recipients list. You may see several listings for a person in the search results screen as you type. To remove several listings, hold down the Command key while you select multiple entries. Then, click the Remove From List button.

Remove Previous Email Addresses From Contacts Card

If you’ve entered information for individuals on a Contacts card, you can’t delete their old email addresses using the Previous Recipients list. For those people, you must open the Contacts application. Locate the individual’s card and manually remove the old email information. If you want to confirm that the email address has been removed, open a new email and enter the recipient’s name in the To field. You won’t see the address you just removed in the list that appears.