What can a former employer legally disclose regarding reasons for
resignation / termination in the state of Massachusetts?

Greetings,
It is not entirely clear what you mean.  Are you asking what
information a former employee could mention if asked for a
reference/recommendation about an employee who was fired  - or maybe
resigned for reason?

Basically...yes..or possibly....resigned in lieu of termination. For
example if i hypothetically were given the option to resign rather
then be terminated for say....harrasment, just as an example. And now
i apply to another company who asks for job history and i list this
previous employer and they contact them, can they disclose exactly why
I resigned. That is more or less my question. With the senario taking
place in Massachusetts. If you need further clarification just let me
know.