Beware Cookie Sharing in Cross-Zone Scenarios
The Problem
From time to time, various users have complained to the IE team that they’re
unable to log into assorted websites and services that they care about: Hotmail
and GMail are two common examples. They report that after entering their
credentials into the login page, the page seems to get caught in some sort of
redirect loop, redirecting from the login page to the site back to the login
page. This pattern either continues endlessly or until an error message is
displayed.
Source : IEInternals
