And...from what I see now...on the Delta website...

"For our airline partners, send a copy of your airline ticket/ticket receipt and boarding pass(es) to:
Delta Air Lines, Inc.
SkyMiles Account Support
Dept. 654
P.O. Box 20532
Atlanta, GA 30320-2532
or fax: 404-773-1945"

No email. Only fax.

If that's not nostalgic...