Is this defamation ?

Good day all, My boss resigned last month and before he left he sent a letter about myself and one college to our chairman, this letter stated that we got a previous boss fired( we did not as she was fired by higher powers due to theft) he said we were racist ( but all our clients of all races praise us ) he also said that we were shown favourtism by higher powers and thus were promoted by them faster ( he was the one who promoted both of us and my promotion i declined and was told i had no choice i had to take it by him) baring in mind during his management of us he threatened to kill me and my collegue and threaten to take us to a hearing with no previous cases laid against us. this has caused us both to be spoken about negatively by our chair man due to false accusations. as nothing mentioned in the letter was true . help please