Business as usual. Keep quiet and head held high. Unless he told the offensive comment TO YOUR FACE, it was not intended for you to hear. Even then keep quiet because it’s a legal he said-she said issue to prove. If he is stupid enough to PUT IT IN WRITING (e-mail is writing) then you have something. People follow their prejudices and bad experiences and transfer these feelings onto other people.
Calm it down! Don’t do anything stupid and quick.