Secondary email

I have a secondary email account from which I forward emails to my primary account so I monitor them at the same time.  I would like to have them replicated, not forwarded so if there is a message I can keep those in that account and reply to them using that account email address.  If this is currlay ply possible, please advise, but your online customer service rep couldn't figure out how to do it and was surprised that the functionality does not seem to exist.  Thank you.