So you just got your 50 items in 20 secs and you're there clicking like a monkey on the mailbox for the next 40 seconds, we're (well at least I am) all been there and feel your pain, but I'm presenting you a nice little trick that works best with fast hard drives (SSDs are even better) on powerful computers since that command tells the game to reload the whole interface and in the process it syncs again with the server (I guess that the 1 minute delay is there to prevent balancing issues or mailbox eploits)
Simply type "/reload" and the mailbox will be there free to use in a few seconds.
This command can me macroed with ease and it's best used with the addon postal and another macro consisting in those commands:
/script CheckInbox(1)
/click PostalOpenAllButton
mash that macro and you'll open the mailbox if your toon is at range and will open all your messages.
Saving those 15 seconds each time means saving up several minutes a day if you're a mass poster
PS This is not my work, I'm merely reposting what I've found on Kevmar's old blog (my auction banker)
PPS I searched "/reload" and didn't see anything related on the first page, sorry if it's a repost