Gmail uses # when you click on a mail to distinguish the page (+ Ajax action).
http://mail.google.com/mail/#inbox/1238e709e37a1394
I found:
Google using # instead of search? in URL. Why?
In FF or Chrome you can use Forward and Back without refresh between those urls:
http://X.com/MyPage.aspx#1
http://X.com/MyPage.aspx#2
http://X.com/MyPage.aspx#3
But on IE the page refresh and it doesn’t count the params after # when a back action is made.
How Gmail make the magic happens?
This is what I was looking for:
http://nix.lv/history/demo.html#3
Found it on:
Save the anchor in the ie6 history