If you are using Yahoo mail, you can get one more mail id , with out creating an extra inbox. This will create a new email address, which you can use even as the primary email address.(Yahoo introduced this option when they started allowing . (dot) in the email address)

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For this Go to Options after logging in to the yahoo mail

Choose mail address from the option menu

Choose Get Stared from the bottom of the page

Choose your additional email address

You can make this email address as primary also.  For this again go to options ==>mail address and select the new address and click on the "Make default" on the right side, where the details of the email address displayed.