No, we can't be completely sure that "The official Twitter of THE MAILMAN" is actually Karl Malone's account. He's not verified, unlike some very famous people that actually deserve that designation, and we hadn't heard that Malone was even on Twitter, bashing things out to his 7,000-plus followers. Then again, the bio behind the account lists Malone's location as "in the woods or in a boat," and it includes tweets like these. So it's probably him.
So we were well pleased that, on his birthday, the fine minds at SLC Dunk alerted us to Karl Malone, on his birthday, responding to his birthday wishes in the exact way that you'd assume that Karl Malone would. Take a look at the tweet: