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