After a lot of R&D I was able to find the solution. Many people posted like go to Settings > Mail > Accounts and then select an account and then you see a button at bottom to delete account. But this was only working for iCloud, Exchange and Gmail in my case.
After a lot of hit and trial I came to know that this account was being configured using automatic profile so this might not delete in this way. So here is the way how I was able to delete that account
Settings > General > Profiles > Select profile > delete profile
In my case this email account was configured as a profile and the above thing work for me very well.
I hope this might help someone.
Thanks for considering.