Hello Ankit as you wish to set Google Apps Email custom login page so you can use gControl directory for Google Apps. It is particularly developed for administrators to provide and control user rights in Google Apps domain, this included add-in will help in correct customization of login (Sin in) page settings.
Get Complete Admin Control by using gControl Directory:
Domain Setting – Add different Google Apps hosted domains, admin also can monitor all domains after creating them sub-domains in main domain. Loin Setting- Get default login page and also option to create a custom login page. Admin can also set a landing page for Google Apps domain. Password Policy- By using gControl enable password policy and set login restrictions for single or multiple users. Forgot Password Policy- After using this option you can set restrictions for forgot password and also number of questions and attempts. (Option to create a new security question) Time Restriction Policy- By using this option admin can apply time restrictions for particular users also an option to set force logout. IP Restrictions- This is highly used feature of directory that allows admin to assign single or multiple users with a particular IP address. Broadcast- To set a message as a broadcast for any particular or multiple users by selecting desired frequency. Get a View: https://www.cloudcodes.com/gcontrol/