The answer may vary slightly by the jurisdiction in which your company operates, but from what I have learned over the years, here's what I do:
- I never respond verbally, I only respond in writing.
- I always require that the entity sending the request do so in writing, and that they also include some form of blanket authorization signed by the former employee.
- I never provide more than dates of employment and last position held, in my written response
However, if the former employee left under bad circumstance, and if I know the owner of the entity making the request, I will call that owner on the phone and ask whether he or she would like to go out for coffee...
Here's a trick I use when I'm trying to get a reference out of a former employer that my company is trying to hire: if that former employer has a policy similar to ours, and will only give dates of employment and last position held, I will try to talk with a supervisor or HR manager and ask if there's any way they can help me. If they say no but seem to be sorry about that, I will ask them, "Let's try this: think about that former employee for a moment. Do you have a mental picture of them now?" and if they say, yes, they do, then I ask them, "Well, are you smiling or are you frowning?" Every once in a while that one will connect with the person on the other end of the line, and they'll cooperate with me by answering my question.