Sometimes Apple Mail will insist on providing an incorrect address for a person when you type their name, or start typing their email address, when filling in the "To" field of a new email. This is usually caused by an accidental incorrect address being used in the past, and that being remembered and re-used for future emails to the same person.
Mail stores all the email addresses of people you have sent messages to in a database called "Previous Recipients". You can edit this and remove incorrect addresses by following these steps...
In Mail: Go to the "Window" menu, and choose "Previous Recipients". Type part of the person's email address in the search area. Note: avoid typing anything which is part of the error. When you see the entry to be deleted, click it. Click the "Remove from list" button.
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