The habit of taking with milk with tea seems to have its origin amongst a segment of the French elite. In 1685, Philippe Sylvestre Dufour devoted a lengthy passage to le Thé au lait -tea with milk-, which he recommended as an antidote against coughs and digestive disorders.
The Chinese black teas imported into colonial Boston surely would have tasted better with milk. The milk would have smoothed out the rough edges of the teas that were already stale by the time they made their years-long journey from Canton via London.
Much of the tea produced today in India, Sri Lanka, and Kenya is manufactured to be drunk with the addition of milk. Milk complements a malty Assam or full-bodied Sri Lankan black tea, but cream can sometimes mask the taste of quality black teas. It’s too heavy.