A Methmail invite will prove that you were invited, but not who invited you. One caveat: when the link could be guessed from timing. How we got here is in How we caught ourselves overpromising. This note is about how it will work and what it will cost us.
Why invites
Methmail will open first as a closed beta, by invitation. That way we can warm up email delivery, keep spam out and help people move their mail by hand. More on the beta on How to get in.
The invite will also stand in for a phone number: you won’t need one to sign up. Sometimes your browser will solve a small computational puzzle: this is how we stop bots without tracking you.
How it will work
We won’t know who invited whom. The invite code will be created on the inviter’s device, and our server will certify it blindly, without seeing the code, so it can’t link the code to the person who issued it or to the person who uses it. One caveat: when the link could be guessed from timing.
In plain words: your device will make up a random code and send it to the server masked. The server will certify it without seeing what it certifies, and your device will remove the mask. When someone comes with the code, the server will be able to check that it certified the code itself, but not whom it certified it for (the scheme is called a VOPRF).
So that a code can’t be used twice, the server will keep a hash of each used code. Who issued it and who used it won’t be recorded.
Methmail will check the server’s answer against a public key from the key log, so the server can’t quietly mark a single inviter with a key of its own.
What will stay visible
The server will see when an account takes an invite and when someone uses one. If hardly anyone else takes or uses invites around that time, the link could be guessed from timing.
So the link gets harder to guess the more invites are taken and used around the same time. If this matters to you, don’t rush: the more time passes between taking an invite and using it, the more other people’s invites will likely fall in between.
What will be kept in the meantime is listed in the inventory, under invitations.
What it will cost
- No rewards for inviting friends. We won’t know whom you invited, so we won’t be able to reward you for it either.
- A lost invite can’t be traced. An invite will work for whoever has it. We won’t learn whom you gave it to or who passed it on. Your device will remember which codes you issued.
- Invites count when issued. An invite will count as used when you create it, not when someone uses it: we’ll have no way to know who used it.
- There will be few invites. Each member will get only a few invites: links or QR codes. Each will be valid for 30 days and work once. There will be few on purpose: that way no one can create mailboxes in bulk. Invite people you’re ready to vouch for: it’s a request, not a check.