Field Notes

entity

JMAP

StatusStableUpdatedStands on3 sourcesSupportsnotes

JMAP (JSON Meta Application Protocol) is an IETF standard protocol for synchronising mail, calendars, and contacts between a client and a server. It is defined in RFC 8620 (core) and RFC 8621 (mail), published in August 2019, and developed primarily by Fastmail.

Design

JMAP uses HTTP and JSON, making it straightforward to implement in web and mobile environments without the legacy complexity of IMAP. It provides efficient batched access: a client can fetch a mailbox listing, message metadata, and message bodies in a single request, rather than issuing dozens of sequential IMAP commands.

Key properties that distinguish JMAP from IMAP:

  • Messages have stable IDs that do not change when moved between mailboxes; a message can belong to multiple mailboxes simultaneously, exposed as labels rather than folders.
  • Push notifications are built into the protocol rather than layered on top.
  • It supports the same data model as IMAP for server-side interoperability, so a server can expose the same mail store over both protocols simultaneously.

Relevance to encrypted email

Open standard for federated e2ee email identifies JMAP as a candidate transport layer for a modern encrypted email standard. A JMAP-based mail system with end-to-end encryption could avoid IMAP’s legacy constraints while preserving federation through the existing email infrastructure. Fastmail already operates JMAP at scale, demonstrating that the protocol is deployed and mature, not merely specified.

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