N1 supports connecting to all the major email providers, as well as pretty much every obscure IMAP server run by your ISP! What's pointed out in the FAQ is just that it uses a cloud service component (also open source! http://github.com/nylas/sync-engine) that we developed first to make it easier to build clients.

Warning to anyone trying to self-host:

Despite N1 calling their cloud engine "open source", the authentication part isn’t – and isn’t included.

If you set up the open source variant yourself, you’ll end up without any authentication.

When you say authentication, do you mean the cloud engine doesn't authenticate against your email providers, or that the desktop client doesn't authenticate against the cloud engine?

I mean that there is no password between desktop client and the open source cloud engine – anyone can log in to it just like that.

The tokens to auth are world-readable under /accounts or /n

This sounds like a job for Sandstorm.io...

Or like any firewall, Nginx config, VPN, etc. Everyone picks a different way to do it, so it's not included in the default sync engine.

Looks really nice, but what's this creepy right sidebar (which obviously lists wrongly guessed pseudo-contacts)?

https://www.dropbox.com/s/bv82he6wlcea3d2/Screenshot%202016-...

Looks like it cannot be disabled?

You can click the button in the top right to close it.

Right now that data comes from FullContact. If it's wrong, you can write them to dispute/update it. https://support.fullcontact.com/knowledgebase/articles/47266...

Okay, just tried myself, adding IMAP/SMTP accounts is supported.