I am referring to how the big players (Google with Gmail, Microsoft with Hotmail, and I suspect many others) tend to flag as spam, or even outright reject your email, as soon as the IP comes from a "little player", such as residential IP, or even virtual private hosting IPs.

Sending an email to a user of such networks has become difficult —at least, more difficult than it should be. Unless of course you come from one of those huge networks. And of course, the users themselves don't see any problem with this: they assume that if you can't send an email to them, the problem must be on your end —not, say, Gmail's spam filter.

On the other hand, if everyone had a little box that send email directly from home, nobody would ever dare to block them.