Parse BCC'd recipient emails correctly

[akrantz01]

Whenever we are sent an email that was BCC'd, we fail to parse the recipients in the To header as it is not a valid email address. In a BCC email, the recipients in the To header are set to undisclosed-recipients:; and the actual recipient is set in the Bcc header.

We should be able to handle BCC'd emails by setting the To field to the contents of the Bcc field if the To field contains undisclosed-recipients:;. However, it would need some extra testing.