hook_mail_alter

We recently did a site for a client that allowed patients to submit a webform to request an appointment. The user could choose their physician and based on their choice, the submission would be emailed to the chosen doctor's secretary. I originally thought about using the key part of the key|value pair for the select list to store the secretary's email address, with the doctor's name. This wouldn't work, however, because the key could not contain standard email address characters. Read on for the solution...