How can i add multiple main accounts in my outlook i tried but i cant access rediffmail.com

I am assuming you know how to add a second account. Things you need to check, sometimes the username wants the domain name as well. For example, if your email address is test@rediffmail.com, your username will be test@rediffmail.com.
Another thing to look for is the ports rediffmail.com uses for incoming and outgoing email. Outlook will use the defaults, a lot of mail providers will not accept the defaults thus not allowing you to connect. Double check with rediffmail.com the ports you need to configure.