You have already been really useful to me here trying to understand the logistics of ip addresses - although I do appreciate its not always straight forward of course.
However, generally speaking:
If I email you from 18.104.22.168 - is it likely that a different person, elsewhere, could also email you from this ip? (generally, I mean) ?
very possible, can be likely, depending on the type of connection
if it's a starbucks or some other lobby free wi-fi type place, then a lot of people could be emailing from the same IP