me, to myself, unbidden: I feel a little bad calling them milkmen but there really is nothing gender-neutral that's still short and snappy and right. culturally, they are milkmen. your milkman delivers the milk in the wee hours of the morning and if you learn anything about them as it pertains to their gender it's probably just their first name at the end of a printed note that gets left with the milk around christmas.
it's just so culturally ingrained. pratchett would probably say that while a person can apply for the job regardless of gender, while they're on it, unseen by anyone and only heard by of the soft hum of the milk float or the clink of the bottles, it's the milkman people think of, and it's the milkman people thank.
(actually I'm suddenly wondering if this is, in fact, something pratchett's included in one of his stories I haven't gotten to yet, because it's exactly the kind of odd british culture thing that a) has lore to it and b) feels weird to talk about.)
you don't talk about your milkman. you pay them and you give them space to do their nightly work. but you should, if you're a decent sort, leave them a tip or small gift around the holidays.