1) Short positive letter should suffice. Details of specific persons would be good. Just make sure the person was helpful and did not bend any DL rules to help (don't want to get that person in possible trouble).

2) Send it via Delta.com http://www.delta.com/emailus/servlet/EmailUs?cmd=go

3) You'll receive a response from DL. It is my understanding that praise and compliments are passed on.

4) After F, Medallions, Bulkhead and Exit Row, plane is boarded back to front.

This post reminds me. I wish DL would bring back the certificates that PMs received 2 years ago. It was nice being able to immediately recognize those that went above and beyond.