Sendmux Email Inbox API + Sending

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Edit Saved Draft

mailbox_update_draft

Edit a saved email draft without sending it; pass the draft ID and expected revision, and reload after a conflict before retrying changes.

Instructions

Edit a saved draft without sending it. Requires mailbox.read and mailbox.drafts.write. Pass the reviewed expected_revision; reload after a conflict before making another edit.

Input Schema

Name	Required	Description
`cc`	No	Visible copied recipients.
`to`	No	Primary recipients; at most 50 total across To, Cc and Bcc.
`bcc`	No	Hidden copied recipients.
`from`	No	Authorised sender; defaults to this inbox.
`draftId`	Yes	Stable draft ID.
`subject`	No	Subject; may be empty.
`If-Match`	No	Current draft ETag; expected_revision is also required.
`reply_to`	No	Authorised reply addresses; defaults to this inbox.
`html_body`	No	HTML body, preserved when saved.
`text_body`	No	Plain-text body.
`mailbox_id`	No	Mailbox public ID to target when the credential grants access to more than one mailbox. Omit when the credential is scoped to exactly one mailbox.
`attachments`	No	Attachments and inline images.
`custom_headers`	No	Custom X-* headers. Writes reject X-SES-TENANT, X-SES-CONFIGURATION-SET and X-SES-MESSAGE-TAGS case-insensitively. On updates, omit this field to preserve saved headers, or pass {} to clear them.
`expected_revision`	Yes	The revision that was reviewed; a stale value returns conflict.

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Addedv1.0.17Nov 7, 2026

TDQS

A4.2/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The annotations already mark the tool as a non-read-only, non-destructive, non-idempotent open-world mutation. The description adds useful behavioral context beyond that: required scopes and optimistic concurrency via expected_revision with reload-after-conflict guidance. It does not fully explain how omitted fields are handled on update, which keeps it from a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the core action and differentiated from sending. The permission and concurrency details follow logically with no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

This is a complex 14-parameter mutation with an output schema and detailed parameter descriptions, and the description covers the key auth and revision-conflict behavior. It could be slightly more complete by stating global partial-update semantics for omitted fields, but nothing essential for calling it is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all 14 parameters are already documented in the input schema, including expected_revision, mailbox_id, attachments, and custom headers. The description reinforces expected_revision but does not add meaning beyond the schema's own parameter descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: edit a saved draft. The phrase "without sending it" clearly distinguishes this from send_draft, so an agent can identify the operation without opening sibling schemas.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It provides clear context: use this to modify an existing draft rather than send it, and it names the required permissions and expected_revision workflow. It does not explicitly compare against create_draft, delete_draft, or control_draft_schedule, so it stops short of full when-to-use/when-not guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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