> I have no idea what “mail” is

Not a native speaker. How do you refer to the pieces of paper that the Royal Mail sometimes drop through your letterbox?

Ironically, despite the company being called the Royal Mail, the letters it delivers are referred to as "post".

This is unlike the US Postal Service, which delivers "mail".

Interesting! Thanks.

To be clear, mail and post are the same thing, one is US English and the other UK English, though as you can see from the names of the companies involved, the distinction was not always so clear cut.

The comment claiming not to know what "mail" was clearly struck people as a little dismissive of US English (any native English speaker knows both "mail" and "post", regardless of which one is used locally)