Is email space quota free??
Better ask @adbenitez about that.
Also remember in box size… even when you’re deleting the file on the emailserver as soon as you downloaded it - what happens when you are off-line while people send you stuff?
Right: the inbox gets full and you can’t recieve any messages anymore.
I think keeping that in mind, it makes sense to do the “handshake”/matchmaking over email and let the file transfer be done in a different protocol/by different means.