I'm not sure about PFO via email but I have only ever received offers via phone; I actually was panicking once because a firm had called me and i'd missed it, I asked my parents whether they thought that they'd call to reject; they said "not unless they are exceptionally polite". It was an offer! So i'd generally take a phone call as a good sign!! From the AC's I've attended, I do believe all of them said they do provide feedback calls if there is a PFO to explain why-so maybe that is the call element! I hope this helps and best of luck