Yahoo Mail allows multiple email addresses by having a main or base address and disposable addresses....I don't use Yahoo mail but this link will explain it better than I ever could and you will be able to sort out for yourself just what you need to do....
The one that I want as my main address is the one I use the most, but when I click onto 'my mail', the address comes up that I hardly use, so I have to sign out of that one and into the one I want.
I'm not looking for disposable email address's, just how to have the one I use most as my main address.
Sorry if I don't sound clear, I'm not very good at explaining things like this.