The phrase "Mail can be sent with" is ambiguous. "can always be sent"? no. But, if read as "Mail can (often, usually, generally) be sent with just a postcode

The phrase "Mail can be sent with" is ambiguous. "can always be sent"? no. But, if read as "Mail can (often, usually, generally) be sent with just a postcode and door number" then it's perfectly true of the UK. And that's a great achievement. I've seen far worse postcode systems. Real world naming always has special cases, so no surprise there. This doesn't entirely invalidate the general point.