The Mailbox app might be having long waiting queues but there is a way you can get the Mailbox app right now without waiting.
You need a Jailbroken device, Mailbox app, iFile app(from cydia store).
http://technoblimp.wordpress.com/ has given a complete guide to get the mailbox app right now.
1. Load Mailbox and get a place in line
2. Load iFile
3. Browse to var/mobile/Applications/ and look through all the weird named folders until you find Mailbox. Once you found it go to Mailbox/Library/Preferences/com.orchestra.v2.plist
4. Tap on com.orchestra.v2.plist and open it with the Text Viewer
5. Scroll towards the end of the document and locate the following lines:
6. Tap on Edit ( upper left corner ) and change the last line from false to true. Save the file. Load Mailbox and enjoy.
Disclaimer : This is an unethical way to get Mailbox and you should not perform unethical actions. This post is for information purposes only.