Ok, not sure if I missed it, but was there a "reply" button in mail.

I know most of the mail I got was from the system for PVP rewards, but a few I got was from friends and such, but I could never find a "reply" button.

This frustrated me to no ends. as I would have to open up my friends or guild list, go to roster, then click on the player, then down to "send mail" just to reply.

Or did I just miss the poorly hidden reply button?

Yep, welcome to ESO: Basic features missing all over the place.

Nope, still missing. Got a nice mail from someone in the March 14 weekend beta and wanted to reply to it but had to send them a new mail.