Can women be firemen or mailmen?

[DemPGH]

To me it comes down to whether or not it's necessary to make a distinction. "Actor in a lead role" and "Actress in a lead role" is kind of a necessary distinction. Congresspeople, however, would seem to be preferable to Congressmen as an umbrella term since there are women in Congress.

I'd probably say "poets" unless it was necessary to differentiate between a female and male poet. 

[DemPGH]

Chairman is gendered, yes. I have never in any setting seen a woman referred to as a chairman, always a "chair."

Mail man is gendered. It's mail carrier.

Stewardess is gendered. It's flight attendant. And so on.

Not that any of this will actually get you in trouble (in the military it might - I believe women in most branches are referred to as Ma'am). It's just that the direction is toward neutral pronouns, unless, again, it's necessary to make a distinction.