When I add a To: header, why doesn't the recipient receive a copy of the e-mail?

Symptom: I used action_add_header to add a new "To:" (or "Cc:" or "Bcc:") field to a message, or used action_change_header to change the "To:" field, but the message didn't go where I thought it should.

Cause: Changing headers does not change the destination of the email message. That is controlled by the envelope recipient(s) in the SMTP dialog. You will have to use add_recipient and/or delete_recipient to change the destination for a message.