JMAP using & inline ops

RFC 8620 requires each JMAP request to include a using array: the capability URNs that apply to every method call in the batch. If a method belongs to a URN you did not declare, the request is not valid for a standards-following server.

Full envelope vs bare methodCalls

Clients may send either:

1. Full envelope: { "using": ["urn:ietf:params:jmap:core", ...], "methodCalls": [...] }
2. Bare array: [["Email/query", {...}, "q0"], ...] — the host then supplies a default using for the envelope it builds.

Atomic Mail MCP (jmap_request) and AgentSkill / CLI use the same default using when you pass only a bare methodCalls array:

• urn:ietf:params:jmap:core
• urn:ietf:params:jmap:mail

That pair covers Mailbox/, Email/, Thread/, SearchSnippet/, and other types declared under the mail capability. For built-in recipes and when to add more URNs, use help --topic jmap_cheatsheet (CLI) or the MCP help tool with topic jmap_cheatsheet.

Pitfall: submission, identity, and blob methods

If you pass a bare methodCalls array and rely on the default using, extend it whenever the batch uses methods from other URNs, for example:

Methods (examples)	Add to using
EmailSubmission/*, Identity/*	urn:ietf:params:jmap:submission
Blob/upload, Blob/get, Blob/lookup	urn:ietf:params:jmap:blob

Ways to do that:

• Put a full { "using": [...], "methodCalls": [...] } object in ops / your JSON file, with every URN you need; or
• MCP: set the tool’s using input array so it includes submission and/or blob in addition to core and mail when your inline ops need them; or
• Use bundled presets (for example send_mail.json), which already embed the correct using for their method calls.

For a narrative send/read example, see Raw JMAP requests.

Related

Raw JMAP requestsNarrative send and read examplesCode examplesEnd-to-end HTTP in Python, Node.js and curlLocal MCP serverops, ops_file and using in the MCP tool