May be a bit hard to post a letter if you weren't tall enough, or am I misunderstanding things?
It is actually pretty tall - but not so tall a person with arms couldn't reach it. A person in a wheelchair, however, might have difficulty. I think the letter slot is probably at about 66 inches off the ground. (ADA guidelines would have that no higher than 48 inches.) (ADA is "Americans with Disabilities Act" and we copy it in Canada.)