How come???   because your computer sees "Paypal" and "Pay.pal" as two completely different entities.  However, unless you pay attention to details, you may miss that distinction.

It is not uncommon at all to see an e-mail address that looks familiar.... if you only look at the first part.  However, look at what is at the back end of the e-mail address, and it is not at all familiar.  This is one way that I distinguish legitimate addresses from those that are not legitimate.  I won't say my way of seeing things is fool-proof; however, it does help.