JMAP: It’s like IMAP But Not Really

With the new year upon us, I decided it was time to do something ambitious for my Open Source project. This is where I normally quip about never mentioning my project before, even though I literally always do. A new year means new jokes so I’m moving on, and really you should too. Cypht is not just Open Source webmail, it’s like the [COOL THING OR PERSON] of Open Source webmail. And it’s NEW. Well I have been working on it for 5 years but NEW in a relative sense, since time is relative, and really what is time? Anyway, ambitiousness.

There has been a “Support JMAP to replace IMAP/SMTP” request lingering on our Github for almost a year. It’s in the “I’m still interested but effin busy bucket“. Recently the poster of said issue mentioned the JMAP specification will soon be finalized and it might be a good time to give it another look. What exactly is JMAP? Let me verbally circle around it a bit more and I promise I will get there.

I reread the high level bits about JMAP. Then I started digging in, created a new module set, shit-canned that approach because it was stupid, took a different angle, got obsessed, stayed up way too late on weeknights, permanently pinned the docs in browser tabs, filed a couple of Github issues with the Cyrus IMAP project (both of which were mis-configurations on my end), and as of this week – hit the milestone of initial IMAP/JMAP compatibility.

Again, what the hell is JMAP? As we all know there are two widely adopted protocols for getting your E-mail to your eyeballs: POP3 and IMAP. POP3 was designed to work with systems that are not always online because that really used to be a thing. IMAP is awesome unless you write code for it in which case it will ruin you. Regardless IMAP is the common standard these days. It’s complicated and old and hard. Why can’t there be a modern REST like API that can do everything IMAP does but better? Astute readers may have added this up by now, but just to clarify: JMAP is a modern REST like API that can do everything IMAP does but better.

The driving force behind JMAP from what I can tell is Bron Gondwana, the CEO of FastMail. As a subscriber to the IMAP protocol mailing list for the last 15+ years (also an actual thing), I recognize Bron from many informative replies to befuddled posters about the IMAP protocol, or the Open Source Cyrus IMAP server he contributes to.

I would like to take my remaining time and open up the floor to questions, so fire away.

Internet: So what is the JMAP API like?

Me: I’m not going to sugarcoat it, JMAP is complicated. But it is really (really) well designed. JMAP is a REST API so it uses HTTP requests and responses to issue commands and get the results. Almost all requests in JMAP are to the same URL using an HTTP POST to submit a JSON body of “methods”. A method is an action or query you want to perform like “give me the 20 newest messages in this mailbox” or “flag this important message from a Nigerian prince”. Also they have excellent docs. Sometimes you have to jump around to piece together what you are looking for but it’s pretty comprehensive.

Internet: How is JMAP better than IMAP?

Me: My top 5:

  1. JMAP is sane
  2. JMAP is not designed around a persistent network socket, so it’s perfect for webmail clients that connect, do stuff, then disconnect (which is exactly NOT how IMAP is supposed to be used)
  3. JMAP finally brings pagination support into the picture. This alone is a huge performance boost
  4. JMAP allows you to chain methods together with back-references to earlier methods. This allows you to combine queries and actions into a single API request. I have not really used this yet because my initial implementation is mimicking the more inefficient patterns of IMAP, but I think this is the single coolest part of the JMAP API design.
  5. Uids in JMAP are globally unique. I don’t need to select a mailbox then fetch the content for a uid in that folder – I can just fetch the content for a uid as it’s unique across folders.

Internet: Do you think JMAP will really take off?

Me: JMAP is an open, smart, modern, and powerful E-mail protocol, so probably not. Short of the ground breaking (not really) Cypht webmail program, I would say JMAP is the best thing to happen to E-mail in a LONG time. JMAP also supports calendars and todos and contacts and sending outbound E-mail and push notification and state management and deltas and other things I can’t remember. Right now development versions of the Cyrus IMAP server support JMAP, and FastMail is using it in production for some of their users. I hope it takes off because as an E-mail client writer it’s been an absolute pleasure to work with.

So sorry to say, we are out of time! To conclude I want to thank the Cyrus IMAP developers for prompt and helpful replies to my uninformed questions. JMAP may not be the future of E-mail, but it should be. It’s like IMAP but not really. It’s better.