Combine dry ingredients in a large mixing bowl; make a well in center of mixture. Combine molasses and milk; add to dry ingredients, stirring just until moistened. Stir in raisins.
Pour batter into a well-greased 1 1/2-quart pudding mold, and cover tightly with a lid. Place mold on rack in a large kettle; add boiling water, filling kettle half full. Bring to a boil; cover and simmer 3 hours.
Remove mold from kettle; remove lid from mold to allow steam to escape. Cool slightly. Loosen bread from sides of mold, and invert onto serving dish. Cool completely.