Unless you are executing a deed or an agreement in relation to land, it is possible and often desirable to have the signatures done remotely or electronically via email. I won’t discuss the vagaries of fax, because fax is a backwards technology. So how do email signatures work, are they enforceable?
Under general contract principles, once a party indicates agreement, that is all that is needed. That person can agree by action or even words. Signing on the dotted line is not strictly necessary. Based on this principle, having a party sign on the signature page and then emailing the signature page to you is sufficient so long as the party had seen the entire final contract. It is best if the party also later sends the original signature page to you as a precautionary measure so it can’t go back on its words.
Deeds and land contracts may have witness and other requirements and it is dangerous to rely on email signatures, pre-signed signature pages or other non-face to face means of execution.