mail-mcp

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smtp_send_message

Send a new email via SMTP. Before calling, show the user a full preview (To, CC, BCC, subject, rendered body, attachments) and get explicit confirmation.

Instructions

Send a new email via SMTP. Before calling, show the user a full preview (To, CC, BCC, subject, rendered body, attachments) and get explicit confirmation.

Input Schema

Name	Required	Description	Default
`cc`	No	CC recipients (optional, max 50)
`to`	Yes	Recipient email addresses (1..50)
`bcc`	No	BCC recipients (optional, max 50)
`subject`	Yes	Email subject (1..998 characters)
`reply_to`	No	Reply-To address (optional)
`body_html`	No	HTML body (at least one of body_text or body_html required). Separate field from `body_text`: pass the HTML itself, never wrapped in pseudo-tags like `<body_html>`; the server rejects them.
`body_text`	No	Plain text body (at least one of body_text or body_html required). Separate field from `body_html`: never concatenate the two or wrap content in pseudo-tags like `<body_text>`; the server rejects them.
`account_id`	No	Account identifier (defaults to `"default"`)	default
`references`	No	References header for threading (optional)
`attachments`	No	File attachments (optional, base64-encoded)
`in_reply_to`	No	In-Reply-To message ID for threading (optional)

Output Schema

Name	Required	Description
`data`	Yes	Tool-specific data payload
`meta`	Yes	Execution metadata (timestamp, duration)
`summary`	Yes	Human-readable summary of the operation outcome

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv0.6.0Oct 22, 2026

changedInput schema / properties / body_html / description

Previous value: -"HTML body (at least one of body_text or body_html required)"New value: +"HTML body (at least one of body_text or body_html required).\nSeparate field from `body_text`: pass the HTML itself, never wrapped\nin pseudo-tags like `<body_html>`; the server rejects them."

changedInput schema / properties / body_text / description

Previous value: -"Plain text body (at least one of body_text or body_html required)"New value: +"Plain text body (at least one of body_text or body_html required).\nSeparate field from `body_html`: never concatenate the two or wrap\ncontent in pseudo-tags like `<body_text>`; the server rejects them."

First observedv0.4.12Sep 9, 2026

TDQS

A3.6/5.0

Behavior3/5

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

With no annotations, the description carries the full behavioral burden. It usefully discloses a mandatory preview-and-confirmation safeguard before sending, but it does not explicitly state that the send is immediate and irreversible, nor does it describe authentication, rate limits, or failure behavior.

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?

Two sentences, front-loaded with the action and followed by the critical pre-call requirement. Every sentence earns its place with no repetition or 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?

Given the rich input schema and the presence of an output schema, the description covers the essential purpose and the key safety gate of preview plus explicit confirmation. The main remaining gap is that it does not explicitly warn that sending is irreversible, but the confirmation requirement substantially mitigates that omission.

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 the input schema already documents all 11 parameters, including recipient limits, body format constraints, and attachment handling. The description's mention of To, CC, BCC, subject, body, and attachments reinforces the preview fields but adds no semantics beyond the schema.

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

Purpose4/5

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

The description states a specific verb and resource: 'Send a new email via SMTP.' The word 'new' distinguishes it from reply/forward siblings, and 'via SMTP' distinguishes it from EWS/Graph send siblings, but it does not explicitly name those alternatives.

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

Usage Guidelines3/5

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

It gives a clear pre-call workflow: preview all fields and get explicit confirmation. However, it does not say when to use this tool versus draft_send, smtp_reply_message, smtp_forward_message, or the EWS/Graph send variants, leaving selection guidance implied rather than explicit.

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