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apple-mail-mcp

by sweetrb
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reply-to-message

Send a reply to an existing email by ID, keeping thread headers intact. Optionally reply to all recipients or save as draft for review.

Instructions

Use when: replying to an existing message by id, preserving its threading headers. Set replyAll for all recipients; set send=false to save as a draft instead of sending. Returns: a confirmation that the reply was sent or saved as a draft; over SMTP, also whether a Sent-folder copy was filed (sentCopy). Do not use when: composing a brand-new message (use send-email / create-draft) or forwarding to new recipients (use forward-message). Safety: with the default send=true this SENDS real email immediately and cannot be unsent — require explicit user confirmation of the recipients and body, or pass send=false to let the user review.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
idYes
bodyYesReply body (plain text; HTML tags such as <br> are not rendered)
sendNoSend immediately (false = save as draft)
replyAllNoReply to all recipients
transportNoSMTP sends clean MIME and preserves reply threading; requires SMTP configuration. AppleScript uses Mail.app and may quote-wrap the new body on macOS 15+. Omit to prefer configured SMTP when sending; drafts use AppleScript. A selected SMTP transport never silently falls back. SMTP with send=false is rejected.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
idNo
okNo
sentNo
sentCopyNoSMTP only: whether a best-effort copy was filed to the account's Sent mailbox over IMAP (issue #220). Absent when no configured IMAP account matches the SMTP identity — not a failure, the feature simply wasn't engaged.
messageIdNo
transportNo
sentCopyErrorNoPresent only when sentCopy is false: why the Sent-folder copy failed.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv2.19.12
    • addedInput schema / properties / body / description
      Added value: +"Reply body (plain text; HTML tags such as <br> are not rendered)"
  2. Changed2 schema fields changedv2.18.0
    • addedOutput schema / properties / sentCopy
      Added value: +{
+  "description": "SMTP only: whether a best-effort copy was filed to the account's Sent mailbox over IMAP (issue #220). Absent when no configured IMAP account matches the SMTP identity — not a failure, the feature simply wasn't engaged.",
+  "type": "boolean"
+}
    • addedOutput schema / properties / sentCopyError
      Added value: +{
+  "description": "Present only when sentCopy is false: why the Sent-folder copy failed.",
+  "type": "string"
+}
  3. Changed3 schema fields changedv2.17.8
    • addedInput schema / properties / transport
      Added value: +{
+  "description": "SMTP sends clean MIME and preserves reply threading; requires SMTP configuration. AppleScript uses Mail.app and may quote-wrap the new body on macOS 15+. Omit to prefer configured SMTP when sending; drafts use AppleScript. A selected SMTP transport never silently falls back. SMTP with send=false is rejected.",
+  "enum": [
+    "applescript",
+    "smtp"
+  ],
+  "type": "string"
+}
    • addedOutput schema / properties / messageId
      Added value: +{
+  "type": "string"
+}
    • addedOutput schema / properties / transport
      Added value: +{
+  "enum": [
+    "smtp",
+    "applescript"
+  ],
+  "type": "string"
+}
  4. Changed2 schema fields changedv2.10.24
    • changedInput schema / $schema
      Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"
    • changedOutput schema / $schema
      Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"
  5. Changed1 schema field changedv2.10.8
    • changedOutput schema / additionalProperties
      Previous value: -falseNew value: +true
  6. Addedv2.8.14
  7. Removedv2.8.10
  8. First observedv2.6.1

TDQS

A4.9/5.0
Behavior5/5

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

With no annotations provided, the description carries the full burden and does so thoroughly. It discloses that send=true SENDS real email immediately and cannot be unsent, requires explicit user confirmation, explains transport-specific behaviors (SMTP vs AppleScript, quote-wrapping on macOS 15+, no silent fallback, SMTP+send=false rejected), and describes the return value (confirmation, sentCopy over SMTP). This is exemplary behavioral disclosure.

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?

The description is compact and front-loaded: the primary use case and key flags appear in the first sentence, exclusions in the second, and safety in the third. Every sentence earns its place, and the structure mirrors how an agent would evaluate the tool: when to use, what it returns, when not to use, and what to be careful about.

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

Completeness5/5

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

Given the tool's complexity (5 params, transport enum, send/draft behavior, safety implications) and the absence of annotations, the description is complete. It covers selection criteria, parameter semantics, return values, safety, and edge cases (SMTP+send=false, AppleScript quote-wrapping). An agent has everything needed to invoke it correctly and safely.

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

Parameters4/5

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

Schema coverage is 80%, so the schema already documents most parameters. The description adds meaningful context beyond the schema: it explains the threading-header preservation purpose, the safety implication of send=true, and the transport-specific behavior of SMTP vs AppleScript. It doesn't add detail for id beyond the schema, but the schema already covers it well.

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 opens with a specific verb and resource ('replying to an existing message by id') and immediately distinguishes itself from siblings by naming send-email/create-draft and forward-message as the tools NOT to use. This makes the tool's scope unmistakable.

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

Usage Guidelines5/5

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

The description explicitly states when to use the tool ('Use when: replying to an existing message by id'), when not to use it ('Do not use when: composing a brand-new message... or forwarding'), and names the alternative tools. It also gives conditional guidance for send=false and replyAll, leaving no ambiguity about selection.

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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