The remarks *may* be considered defamation if:1) They are a factual assertion, not an opinon--opinions are never defamtion (libel or slander) and everyone is legally entitled to have and express opinions. So an email saying that you have a "negative attitude" is not defamation, since a "negative attitude" is not a provable (or disprovable) thing--i.e. it is not a fact. Rather, as something purely subjective, it is an opinion.2) The factual statement must be false, since the truth is a defense to a claim of defamation. So if the email claimed that you made certain specific remarks to students (a factual assertion), but you did in fact make those remarks (so it is true), that is not defamation.