You've waited over three years for it, and it's finally here. You can now private message other users.
There's a link to your inbox up underneath your avatar at the top of the page. You can send text based messages to one or more users by hitting 'Start Conversation'. They'll receive an email letting them know that there's a message waiting for them.
You can opt out of receiving emails by editing your profile and ticking the 'Opt out' box.
Now to just implement ignoring posts by certain users...