Hello Sohaib,
Sorry for being a little annoying, but opening the same topic twice will not solve your problem.
http://forum.mikrotik.com/t/outlook-not-working/58148/1
You have the basic necessary information in the previous topic.
Maybe it is time to read the wiki on how to use NAT and set up routing…
http://wiki.mikrotik.com/wiki/Manual:IP/Firewall/NAT
Check how to do Source NAT.
In my opinion this is a support forum, not a crash course in routing. You have to do your learning/reading part, too.
Stop using your webproxy and get your system working without it first as a simple router with NAT.
Then your outlook will work. Enable webproxy after.