While pondering this question asked earlier today, I started to wonder why post (in the sense of correspondence) is used in British English but not American English.
So I looked up the etymology of mail in Etymonline, seeking information about when the usages diverged.
I found something really interesting that I hadn't known before:
"post, letters," c. 1200, "a traveling bag," from Old French male "wallet, bag, bundle," from Frankish *malha or some other Germanic source, from Proto-Germanic *malho- (cognates: Old High German malaha "wallet, bag," Middle Dutch male "bag"), from PIE *molko- "skin, bag." Sense extension to "letters and parcels" (18c.) is via "bag full of letter" (1650s) or "person or vehicle who carries postal matter" (1650s). In 19c. England, mail was letters going abroad, while home dispatches were post. Sense of "personal batch of letters" is from 1844, originally American English.
So at least up to 19th century, in England, post was domestic or local mail (from the original sense of sticking something to a post in the town square where all the locals could see it), and mail was international mail (because originally that was the stuff you had to give a guy who had a leather bag and wandered around a lot).
Does this distinction between post and mail still exist in contemporary BrE? If not, is there any current distinction between the words? When is each used in modern BrE discourse? If the distinction has waned or the senses merged, when did that happen, and what accounts for he change?
Also, side question: is a mailbox (or any variety) referred to as simply a post (without the -box suffix) in any register of contemporary BrE?
1. For clarification, I am not asking about the different uses of post and mail in AmE vs BrE; this question is solely concerned with BrE, and the distinction, if any, between these words in the UK. AmE is not relevant, here.
2. I'm mostly thinking about England here, but would be interested to hear about usage in any of the other UK countries or Ireland.