Multi Mail

Reply to a message

messages_reply

DestructiveIdempotent

Reply to a message, inside its own thread and quoting it below the reply: to whoever wrote it, or with replyAll to everyone on it. Call this only when the person asked for this message to go; when they asked to prepare one, draft it instead. A request id already spent sends nothing again: the answer says whether that send went or may have gone.

Input Schema

TableJSON Schema

Name	Required	Description
`cc`	No	Who to copy, instead of those replyAll copies.
`to`	No	Who the reply goes to, instead of whoever wrote the message and, with replyAll, those it was sent to.
`body`	Yes	The reply text.
`html`	No	The message as HTML, for formatting; body stays its plain-text version. An Outlook mailbox keeps only the HTML and writes the plain version from it.
`mailbox`	Yes	The mailbox's name or its email address.
`replyAll`	No	Also address everyone the message was sent to and copied - never its blind copies, never this mailbox.
`messageId`	Yes	The provider's own identifier.
`requestId`	Yes	Your own id for this send, new for every message. One whose send went or may have gone sends nothing again.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`id`	Yes
`accepted`	No
`threadId`	Yes
`messageId`	No
`sentCopyKept`	No
`refusedRecipients`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 8, 2026
- addedOutput schema / properties / sentCopyKept
```
Added value: +{
+  "const": false,
+  "type": "boolean"
+}
```

Changed2 schema fields changedOct 8, 2026

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"

Changed1 schema field changedOct 8, 2026
- addedOutput schema / properties / refusedRecipients
```
Added value: +{
+  "items": {
+    "type": "string"
+  },
+  "type": "array"
+}
```

Changed6 schema fields changedOct 6, 2026

changedInput schema / properties / cc / items / pattern

Previous value: -"^(?!\\.)(?!.*\\.\\.)([A-Za-z0-9_'+\\-\\.]*)[A-Za-z0-9_+-]@([A-Za-z0-9][A-Za-z0-9\\-]*\\.)+[A-Za-z]{2,}$"New value: +"^(?:[A-Za-z0-9_'+\\-]+\\.)*[A-Za-z0-9_'+\\-]*[A-Za-z0-9_+-]@(?:[A-Za-z0-9][A-Za-z0-9\\-]*\\.)+[A-Za-z]{2,}$"

changedInput schema / properties / to / items / pattern

Previous value: -"^(?!\\.)(?!.*\\.\\.)([A-Za-z0-9_'+\\-\\.]*)[A-Za-z0-9_+-]@([A-Za-z0-9][A-Za-z0-9\\-]*\\.)+[A-Za-z]{2,}$"New value: +"^(?:[A-Za-z0-9_'+\\-]+\\.)*[A-Za-z0-9_'+\\-]*[A-Za-z0-9_+-]@(?:[A-Za-z0-9][A-Za-z0-9\\-]*\\.)+[A-Za-z]{2,}$"

removedOutput schema / properties / id / anyOf

Removed value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]

addedOutput schema / properties / id / type

Added value: +[
+  "string",
+  "null"
+]

removedOutput schema / properties / threadId / anyOf

Removed value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]

addedOutput schema / properties / threadId / type
```
Added value: +[
+  "string",
+  "null"
+]
```

First observedOct 5, 2026

TDQS

A4.7/5.0

Behavior4/5

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

Beyond the annotations (destructiveHint=true, idempotentHint=true), the description discloses concrete behavior: the reply is threaded and quotes the original, and a replayed requestId 'sends nothing again' with an answer that says whether the send went or may have gone. It does not cover other side effects (e.g. whether the reply is stored in Sent) or any permission requirements, so it stops short of 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 sentences, each carrying distinct load: capability/threading, send-vs-draft routing, and idempotency. The core purpose is front-loaded in the first clause and there is no filler or restatement of the title.

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?

For an 8-parameter mutation tool with an output schema, the description covers the decision-critical items: what it does, when to use it versus drafting, recipient defaults, and retry safety. Return values need not be explained since an output schema exists, and nothing an agent needs to invoke this correctly is missing.

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 description coverage is 100%, so the baseline is 3; the description still adds routing semantics the schema does not spell out - default recipients are whoever wrote the message, and replyAll extends that to everyone on it, while cc substitutes for the replyAll copies. It does not elaborate on html/body interplay beyond what the schema already documents.

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?

States a specific verb and resource ('Reply to a message') plus two differentiating traits: it goes 'inside its own thread and quoting it below the reply' and supports both sender-only and replyAll routing. This distinguishes it cleanly from siblings like messages_send, messages_forward and drafts_reply without needing the schema.

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?

Gives an explicit use/do-not-use rule: 'Call this only when the person asked for this message to go; when they asked to prepare one, draft it instead.' That names the alternative path (drafting) and the condition that selects it, so the agent never has to infer whether to send or prepare.

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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