1. Go to the contact card of the person/company where it is linked to.
  2. Right-click on the email address (that should not be mentioned there at CONTACT INFO).
  3. Choose 'Delete'.
  4. Check in appearing popup 'Unlink this email address from this contact too' and confirm.

Now all emails are detached from this person/company, the items no longer appear in its archive and the name no longer appears in your inbox. Link the email address again to the proper contact in for instance your inbox.