Hi, I'm a brand new Surface user ...

I have 3 email accounts which I have set up to deliver to my Surface using Outlook.com. Let's call them:

Mail1
Mail2
Mail3

All 3 are currently delivering to my Mail1 account, as well as delivering to their appropriate folders/accounts on the Surface. This is annoying as the messages are duplicates and requires endless, tedious deletion.

How can I deliver Mail1 only to the Mail1 account, Mail2 only to the Mail2 account, and Mail3 only to the Mail3 account?

Apologies if this is another silly question.
Thanks, Caroline