Ma'am is a good place to start and if you are feeling frisky maybe honey or sweetie...
But with Fed Employs that you, have/are/might ever, have a working relationship with, it is best to stick with Ms/Mrs.
Oh my gosh, that is a major difference between here and the south. When we start getting called maam, it is a very depressing thing. It means you are old, over the hill etc. I really don't care much about what I am called as long as it isn't a bad thing. One old logger will say, "All right dear." It is just the way he is. A stubbie is a beer.