Unlinking my mail from a secondary and seperate...

I have a macbook laptop 2010 useing Sierra ver 10.12.6.

Somehow my mail that goes to my main mailbox seems haven gotten linked or being sent to a secondary mailbox with a different email address. How can I de-link this to fix this problem ?

Check the account on the e-mail provider's web site to see if a forwarding option has been set.