Open source and standards

Fastmail is the leading advocate keeping the email and calendar ecosystems open and interoperable, fighting against the encroaching proprietary capture of the big tech giants in the field.

Standards work

We are proud to be active leaders at the Internet Engineering Taskforce (IETF), M3AAWG, and CalConnect, where we work with other vendors in the industry to make email (and calendars!) better for everyone.

In a world increasingly dominated by closed proprietary messaging systems, such as WhatsApp, iMessage, and Facebook Messenger, email stands alone as an open communication system, not solely owned by a big tech company. This allows for increased innovation and freedom — you don’t have to just use the email client from your email host, you can also choose from a number of others to suit your needs.

For this to work, there has to be standard APIs that everyone adopts. Our work includes leading the design and specification of JMAP — The JSON Meta Application Protocol (RFC8620) — the next-generation sync protocol for building better email and calendar apps. We also contribute heavily to improving the legacy protocols like IMAP, and building industry-wide anti abuse measures.

Open source

As part of building Fastmail, we create a lot of libraries and foundational software. Where we believe these are useful to others, we will often look to open source them to support the wider ecosystem. You can find much of our open source work, large and small, or our GitHub account.


Cyrus is the battle-tested server that stores your email, contacts, and calendars at Fastmail, and supports access via JMAP, IMAP, CardDAV & CalDAV. Originally started by Carnegie Mellon university, it is now deployed widely around the world. Fastmail has been the primary contributor and maintainer for many years, adding JMAP support among many substantial improvements.


Squire is an HTML5 rich text editor, which provides powerful cross-browser normalisation in a flexible lightweight package. It was designed to handle email composition for the Fastmail web app, and now powers the compose for many other webmail systems as well.

Overture JS

Overture is a high-performance JavaScript framework. It takes a batteries-included approach to provide you all the tools you need to create fast, powerful applications on the web. It’s the foundation on which Fastmail’s app is built.

And many more…

Other open source contributions include: Hopscotch, a tiny, high-performance HTTP image proxy; Ix, a modern Perl library for building JMAP APIs; and an Authentication Milter to add all of the email authentication standards to your SMTP milter. Browse all this and more on our GitHub account.

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