Prior to the Northeast merger in 1973, Delta did not serve Boston at all. When they acquired NE, they took over all its gates in Terminal C (then called the North Terminal, also served by TWA and United).
Service was operated to:
Presque Isle/Houlton, ME
Lebanon/White River Junction, VT
Fall River, MA
Martha's Vineyard, MA
Fort Lauderdale, FL
Shortly after the NE acquisition, Delta dropped Lebanon, Keene, Martha's Vineyard, Hyannis, Nantucket, and Fall River -- most of those routes were picked up by Air New England.
In any case, that's how DL
got its Boston presence - after Deregulation it was allowed (finally) to fly to Atlanta - previously pax had to connect in New York, which was another hub for Northeast.