Commands:
/mailbox - View list of mailbox commands
/mailbox open - Open your own mailbox to retrieve items
/mailbox send <player> - Send item in your hand to another player
/mailbox sendmore <player> - Send multiple items to another player (Opens a menu)
/mailbox ignore <player> - Ignore mailbox items from a specific player
/mailbox toggle - Completely disable items being sent to your mailbox
/mailbox open <player> - Open the mailbox of another player (Admins only)

Permissions:
rcmailbox.cmd.mailbox - Access to /mailbox and /mailbox open
rcmailbox.cmd.senditem - Access to /mailbox send <player>
rcmailbox.cmd.sendmore - Access to /mailbox sendmore <player>
rcmailbox.cmd.ignore - Access to /mailbox ignore <player>
rcmailbox.cmd.toggle - Access to /mailbox toggle
rcmailbox.size.x - Access to specific size mailbox. Replace x with number (9, 18, 27, 36, 45, 54)
rcmailbox.admin - Access to /mailbox open <player>