I'm not against mailboxes per se. But it really is a relic by now. Blizzard have even added a ridiculous amount of mailboxes at every major hub, just to make sure you don't have to run far to get to them. What then, I ask, is the point?
It'd be one thing if mailboxes were actually immersive little elements of a cosy world, such as in the Lord of the Rings Online where hobbits have a quest to deliver mail and avoid the prying eyes of eavesdropping hobbits (if memory serves).
But in WoW, they are the one stupid little thing you have to go through a minor hassle to use, when all major features are overly easy to do.
It should be the other way around. Finding groups and travelling should be immersive, a bit demanding, and require that you travel around in the world. Instead they require nothing off you, while mail boxes demand that you find a major quest hub. Nonsense, I think.