Reading mail que manager

When I go into the mail que manager and then click on a particular message (multible mailing)

I find an email list, in alphabetical order, that has starts with either a Y or N (Two entries) before each address.
I'm assuming that the two entries represent Yes or No .....but refering to what?

example:

YY name@name.com
or
NY Name@name.com ??? NN; YN; etc.

How and where can I get an answer to this question?
Thanx