Well, if you look down below...
I think that shows pretty well what the effect of the steadily leaked out DNC emails was on a lot of potential voters, especially the Sanders supporters. There's a ton of that going around lately.
Never mind that hardly anybody read the emails - how could they given the volume? - and that it doesn't appear there was anything terribly bad in the emails, mostly a few Hillary supporters engaging in petty bellyaching about the Sanders campaign - but the public was told it was very scandalous and they should be shocked, so they were.
The leaked emails only had to depress the Democratic voter turnout by less than 100K in a few states to win it for Trump, and it appears that happened, and that's what won it for Trump. (Well, that and voter suppression, and in Michigan apparently a lot of voting machines in black neighborhoods in Detroit mysteriously dropping all votes for President on thousands or tens of thousands of ballots - it's really fucked up that that will never be investigated.)
It's not like the DNC email dump was the only thing that caused Trump's election, but it's one of a number of factors which combined to cause it. Because of comments like the one I quoted (and frequently see elsewhere) I don't think it was insignificant.