I've been using MAC OS X Mountain Lion 10.8.5. How do I request a read receipt when sending e-mail with Outlook for Mac 2011?
Outlook:Mac doesn't have the read receipt feature.
And, frankly, you shouldn't use read receipts. Most mail clients can be set up to simply ignore read receipt requests. If the mail client isn't ignoring read receipt requests, then it gives the reader a message asking if the reader wants to send a read receipt; many people select no. The existence of a read receipt doesn't actually tell you whether your reader read your mail.