How to create email ALIAS, rather than POP account

How to create email ALIAS, rather than POP account

I'm wanting ( needing, really) to set up an email alias (a'la Gmail). I can't see how to do that. If I try to set up an account via Settings > Mail Account > Add Account, it requires mail server info. This email I need an alias for is a forward-only account, not one for which I have POP info.