There is a very good document available to current DL pilots regarding how to submit internals.

Ask your recommender (is that a word??) to log onto the company website and from the flight operations page click the admin tab (on the left), then the Pilot Selection tab (top right). In the center of the page is a link titled "How do I recommend someone for a Delta pilot position?" The document describes, in detail, both the AirlineApps and the direct email recommendation process.

FYI: it does not mention the Delta email address requirement. I followed the directions (sent from a gmail account) earlier this year, included my name/Emp #/base/aircraft/seat in the email and the candidate received an email interview invite 37 days later. (Civilian, 121, PIC, several types, instructor, app was perfect BEFORE I sent email)