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In a comment, John Lawler wrote

In American English, if the -man is stressed and pronounced /mæn/, like mailman, then it's masculine. If, on the other hand, the -man is unstressed and pronounced /mən/, like chairman, then it can be used for either sex. Many people follow this, but individuals often vary, since many English speakers haven't learned that pronunciation is different from spelling, and they may form variant rules, seeking "correctness" from what they learn, or don't learn, in school.

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