I have my turn's password (thx Luthor) - so will play it tonight.
Gmail forwarding only cares about who emailed the turn (ie the 'from' email address) and uses that info to forward to the next player.
The tracker reads the gmail account, find the last valid email (with attachment and from one of the players) and grabs the attachment name. Using the attachment name, it works out who the turn should go to ... and posts that info (hence why the in-game name is important).