One Gmail Account to manage Multiple Accounts

1. Login to your primary gmail account (from where you wish to send/receive mails)
2. Click gear icon on top right of the page
3. Go to "mail settings"
4. Go to "Accounts" Tab
5. Click on "Add a mail account you own"
6. Type in the email address you want to add, and click on "next step" button.
7. Enter the complete user name i.e user@domainname.extension
8. Enter the password of that user
9. In POP server for gmail powered account type: pop.googlemail.com
10. Select port 995
11. Check the second check box saying "Always use a secure connection (SSL) when retrieving mail."
12. Leave others unchecked
13. Click "Save".

Now you can send and receive mails from your other account on this gmail account.

You may add as many email account as you wish.