There is a suspicion – or perhaps a hope – among Trump supporters that Russia has all of Hillary's emails and will release them just before the election.  I don't think so.  Assuming he does have the emails, look at it from Putin's point of view. 

If he releases them, Hillary is toast, he gets the satisfaction of bringing her down, and Trump gets elected.  Then Putin has to deal with Trump for the next four or perhaps eight years.  Despite his voiced admiration for Putin, Trump is strong and unpredictable and will be looking to America's interests pretty aggressively.

Ah, but if he doesn't release them, and Hillary is elected, how things change!  Obama pretty much let Putin get away with everything.  While Hillary might do somewhat better just to prove a woman can be tough, Putin has a trump (ha, ha) card: "be nice, or the emails will show up in cyberspace for everyone to see."  The really scary thing about all this is that Putin doesn't even have to have the emails, so long as Hillary thinks he might. 

Whatever else he is, Putin is a smart operator.  His best move is to do what he can to help Hillary get elected, then start the blackmail.

Note that if China has the emails, similar arguments apply.  China certainly has no reason to look favorably on a Trump presidency.  The only way the emails are likely to be released is if someone other than Russia or China has them and either doesn't want Hillary elected or just wants to create chaos in our election.