Apple Mail

Hi

I have an apple email , I deccide to add another email address so that I could access them in one place.

but now the mails seem to be mixed up . When I send an email from the email I have just added itsend a copy to my apple email . So now I have a number of copies of the same email , in sent box and then coming back to me in the other email

If I delete the copy coming back to me it also deletes it from the other email

Help