How about not using your servers for anything?

Unfortunately, we have to use an intermediate server to use Google OAuth.

If a malicious party successfully attacked the Nylas auth servers, how much of my email data would they be able to get? All of it?

The backend speaks SMTP, IMAP, and HTTP. It is basically a glue (or proxy) between SMTP/IMAP (including those protocols over TLS) and HTTP. Nylas Pro talks HTTP to the glue (I assume that is using TLS, so HTTPS). Nylas Mail also talks HTTP to the backend, but the backend runs locally, so you're self hosting the backend. I suppose this has a performance loss. (With Nylas Pro, you can set a separate backend server if you desire but that requires work. That is a really cool feature for a business though.)

So I would assume you are hosed. The passwords need to be stored plaintext.

I don't think the free version of Nylas Mail is storing IMAP passwords, plaintext or otherwise. For Gmail, at least.

1. You never enter them into the client. It uses Oauth to authenticate.

2. By the comment here, it seems that they're using Google's Gmail API. https://news.ycombinator.com/item?id=13417904

Oh, it does save the password.

Oauth makes sense that there's no password saved. A unique key is saved which is authenticated with Google. If this key leaks, you are hosed, too, but at least you can revoke that key.

I tried grep mypasswd ~/.nylas-mail/* and grep said Binary file shared.sqlite matches. This did not occur in ~/.nylas it makes sense and it is inevitable, a client like Thunderbird suffers from the same.

It can be circumvented by saving the password encrypted and decrypting it using a master password. That is akin to how LastPass and Mozilla save their cloud data.

Using containers etc would also lower the threat.

In a way its good the password is saved locally. The engine also runs locally. It moves the threat model to the client, away from Nylas servers. Kudos.

The app looks great, but I just am not in favor of piping everything I have with email through your servers. Just a standalone app as basic version with opt-in for Google OAUth would justify its use case.