Buffer Overflow Intro. ©2002, Jedidiah R. Crandall, Susan L. Gerhart, Jan G. Hogle.  http://sfsecurity.pr.erau.edu
 Big numbers take multiple mailboxes
If someone wants to store a number bigger than 255, they need multiple mailboxes. 
Four mailboxes means 8 bits x 4 mailboxes = 32 bits.  232 = 4,294,967,296 so you can store numbers in the billions with four mailboxes.