How do you scrape emails?

I've been seeing a few username lists and I would like to know how people scrape emails. When you join a server, you only get the usernames of the player, so how do you get their emails?

Thanks.

EDIT: My bad if this is the wrong section...

up up up up >>>>>>>>>

I can sell you a list with 200k E-Mails unchecked on Minecraft

give me your skype

Look in the tools thingg.. you should see a program that helps you.