Currently, we send lots of e-mail everyday to Support for our
application.

Support in turns assigns a reference number called a Tracker to every
e-mail we send for each of the problems... It could be anywyere from
say e.g. 1000 - 9999...

Say today I send an e-mail for a problem to Support and they reply
with a tracker of 2575 and some further correspondence may be
exchanged related to this tracker among several other mails that has
nothing to do with them.

I want to assign every e-mail I have with the Tracker Number so that I
can sort by the Tracker and see all those e-mail in one place in any
order I want.

Yes.. I can use Category... but I think it is a waste to use several
different categories just for this purpose... All I am expecting is
some kind of Tag or Unique Identifier that may show up on the normal
view and I am free to sort it.

Sample:

From, To, Subject, Received Time, Sent Time, Unique Identifier /
Tag...
Support, ifiaz, Application Problem, 23/09/08 17:00, , 2575
Support, ifiaz, Application Problem2, 23/09/08 18:00, , 3220
Support, ifiaz, Application Problem3, 23/09/08 19:00, , 3020
Other Guy1, ifiaz, Application Problem3, 23/09/08 19:00, ,
Other Guy2, ifiaz, Hi there, 23/09/08 19:00, ,

Can someone help?