Fluxmail

Preview send

preview_send

Read-only

Preview a composed email's resolved sender, recipients, subject, and attachments before sending, so you can verify the message without delivering it.

Instructions

Show the resolved sender, recipients, subject and attachments without sending mail.

Input Schema

Name	Required	Description
`cc`	No	Recipients, each "Name <a@x.com>" or "a@x.com"
`to`	No	Recipients, each "Name <a@x.com>" or "a@x.com"
`bcc`	No	Recipients, each "Name <a@x.com>" or "a@x.com"
`from`	No	Connected address or an available send-as address
`draftId`	No
`subject`	No	Defaults to "Re: ..." when replying
`bodyHtml`	No	HTML body
`bodyText`	No	Plain-text body. Line breaks appear in the sent email. Keep each prose paragraph on one continuous line and separate paragraphs with blank lines.
`replyAll`	No	With replyToMessageId: reply to all original recipients
`accountId`	No	Account to operate on. Optional when exactly one account is connected.
`attachments`	No
`replyToMessageId`	No	Message being replied to; threads correctly and computes recipients if "to" is omitted

Output Schema

Name	Required	Description	Default
`data`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed9 schema fields changedv0.19.0Oct 30, 2026

changedInput schema / properties / accountId / anyOf

Previous value: -[
-  {
-    "minLength": 1,
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "maxLength": 512,
+    "minLength": 1,
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / properties / attachments / anyOf

Previous value: -[
-  {
-    "items": {
-      "additionalProperties": false,
-      "properties": {
-        "content": {
-          "description": "base64",
-          "type": "string"
-        },
-        "contentId": {
-          "description": "Content-ID for an inline image, referenced from bodyHtml as cid:<contentId>",
-          "minLength": 1,
-          "type": "string"
-        },
-        "disposition": {
-          "description": "Defaults to attachment",
-          "enum": [
-            "inline",
-            "attachment"
-          ],
-          "type": "string"
-        },
-        "filename": {
-          "minLength": 1,
-          "type": "string"
-        },
-        "mimeType": {
-          "minLength": 1,
-          "type": "string"
-        }
-      },
-      "required": [
-        "filename",
-        "mimeType",
-        "content"
-      ],
-      "type": "object"
-    },
-    "type": "array"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "items": {
+      "additionalProperties": false,
+      "properties": {
+        "content": {
+          "description": "base64",
+          "type": "string"
+        },
+        "contentId": {
+          "description": "Content-ID for an inline image, referenced from bodyHtml as cid:<contentId>",
+          "maxLength": 255,
+          "minLength": 1,
+          "type": "string"
+        },
+        "disposition": {
+          "description": "Defaults to attachment",
+          "enum": [
+            "inline",
+            "attachment"
+          ],
+          "type": "string"
+        },
+        "filename": {
+          "maxLength": 255,
+          "minLength": 1,
+          "type": "string"
+        },
+        "mimeType": {
+          "maxLength": 255,
+          "minLength": 1,
+          "type": "string"
+        }
+      },
+      "required": [
+        "filename",
+        "mimeType",
+        "content"
+      ],
+      "type": "object"
+    },
+    "type": "array"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / properties / bcc / anyOf

Previous value: -[
-  {
-    "description": "Recipients, each \"Name <a@x.com>\" or \"a@x.com\"",
-    "items": {
-      "minLength": 1,
-      "type": "string"
-    },
-    "type": "array"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "description": "Recipients, each \"Name <a@x.com>\" or \"a@x.com\"",
+    "items": {
+      "maxLength": 512,
+      "minLength": 1,
+      "type": "string"
+    },
+    "maxItems": 100,
+    "type": "array"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / properties / cc / anyOf

Previous value: -[
-  {
-    "description": "Recipients, each \"Name <a@x.com>\" or \"a@x.com\"",
-    "items": {
-      "minLength": 1,
-      "type": "string"
-    },
-    "type": "array"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "description": "Recipients, each \"Name <a@x.com>\" or \"a@x.com\"",
+    "items": {
+      "maxLength": 512,
+      "minLength": 1,
+      "type": "string"
+    },
+    "maxItems": 100,
+    "type": "array"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / properties / draftId / anyOf

Previous value: -[
-  {
-    "minLength": 1,
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "maxLength": 512,
+    "minLength": 1,
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / properties / replyToMessageId / anyOf

Previous value: -[
-  {
-    "minLength": 1,
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "maxLength": 512,
+    "minLength": 1,
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

addedInput schema / properties / subject / anyOf

Added value: +[
+  {
+    "maxLength": 998,
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

removedInput schema / properties / subject / type
```
Removed value: -[
-  "string",
-  "null"
-]
```

changedInput schema / properties / to / anyOf

Previous value: -[
-  {
-    "description": "Recipients, each \"Name <a@x.com>\" or \"a@x.com\"",
-    "items": {
-      "minLength": 1,
-      "type": "string"
-    },
-    "type": "array"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "description": "Recipients, each \"Name <a@x.com>\" or \"a@x.com\"",
+    "items": {
+      "maxLength": 512,
+      "minLength": 1,
+      "type": "string"
+    },
+    "maxItems": 100,
+    "type": "array"
+  },
+  {
+    "type": "null"
+  }
+]

Changed14 schema fields changedv0.18.0Oct 28, 2026

changedInput schema / properties / attachments / anyOf

Previous value: -[
-  {
-    "items": {
-      "additionalProperties": false,
-      "properties": {
-        "content": {
-          "description": "base64",
-          "type": "string"
-        },
-        "filename": {
-          "minLength": 1,
-          "type": "string"
-        },
-        "mimeType": {
-          "minLength": 1,
-          "type": "string"
-        }
-      },
-      "required": [
-        "filename",
-        "mimeType",
-        "content"
-      ],
-      "type": "object"
-    },
-    "type": "array"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "items": {
+      "additionalProperties": false,
+      "properties": {
+        "content": {
+          "description": "base64",
+          "type": "string"
+        },
+        "contentId": {
+          "description": "Content-ID for an inline image, referenced from bodyHtml as cid:<contentId>",
+          "minLength": 1,
+          "type": "string"
+        },
+        "disposition": {
+          "description": "Defaults to attachment",
+          "enum": [
+            "inline",
+            "attachment"
+          ],
+          "type": "string"
+        },
+        "filename": {
+          "minLength": 1,
+          "type": "string"
+        },
+        "mimeType": {
+          "minLength": 1,
+          "type": "string"
+        }
+      },
+      "required": [
+        "filename",
+        "mimeType",
+        "content"
+      ],
+      "type": "object"
+    },
+    "type": "array"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / properties / bcc / anyOf

Previous value: -[
-  {
-    "$ref": "#/properties/to/anyOf/0"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "description": "Recipients, each \"Name <a@x.com>\" or \"a@x.com\"",
+    "items": {
+      "minLength": 1,
+      "type": "string"
+    },
+    "type": "array"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / properties / cc / anyOf

Previous value: -[
-  {
-    "$ref": "#/properties/to/anyOf/0"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "description": "Recipients, each \"Name <a@x.com>\" or \"a@x.com\"",
+    "items": {
+      "minLength": 1,
+      "type": "string"
+    },
+    "type": "array"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / properties / replyToMessageId / anyOf

Previous value: -[
-  {
-    "$ref": "#/properties/draftId/anyOf/0"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "minLength": 1,
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

removedOutput schema / properties / data / properties / bcc / items / $ref
```
Removed value: -"#/properties/data/properties/to/items"
```
addedOutput schema / properties / data / properties / bcc / items / additionalProperties
```
Added value: +true
```

addedOutput schema / properties / data / properties / bcc / items / properties

Added value: +{
+  "email": {
+    "type": "string"
+  },
+  "name": {
+    "type": "string"
+  }
+}

addedOutput schema / properties / data / properties / bcc / items / required
```
Added value: +[
+  "email"
+]
```
addedOutput schema / properties / data / properties / bcc / items / type
```
Added value: +"object"
```
removedOutput schema / properties / data / properties / cc / items / $ref
```
Removed value: -"#/properties/data/properties/to/items"
```
addedOutput schema / properties / data / properties / cc / items / additionalProperties
```
Added value: +true
```

addedOutput schema / properties / data / properties / cc / items / properties

Added value: +{
+  "email": {
+    "type": "string"
+  },
+  "name": {
+    "type": "string"
+  }
+}

addedOutput schema / properties / data / properties / cc / items / required
```
Added value: +[
+  "email"
+]
```
addedOutput schema / properties / data / properties / cc / items / type
```
Added value: +"object"
```

Changed25 schema fields changedv0.15.0Oct 17, 2026

addedInput schema / properties / accountId / anyOf

Added value: +[
+  {
+    "minLength": 1,
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

removedInput schema / properties / accountId / minLength
```
Removed value: -1
```
removedInput schema / properties / accountId / type
```
Removed value: -"string"
```

addedInput schema / properties / attachments / anyOf

Added value: +[
+  {
+    "items": {
+      "additionalProperties": false,
+      "properties": {
+        "content": {
+          "description": "base64",
+          "type": "string"
+        },
+        "filename": {
+          "minLength": 1,
+          "type": "string"
+        },
+        "mimeType": {
+          "minLength": 1,
+          "type": "string"
+        }
+      },
+      "required": [
+        "filename",
+        "mimeType",
+        "content"
+      ],
+      "type": "object"
+    },
+    "type": "array"
+  },
+  {
+    "type": "null"
+  }
+]

removedInput schema / properties / attachments / items

Removed value: -{
-  "additionalProperties": false,
-  "properties": {
-    "content": {
-      "description": "base64",
-      "type": "string"
-    },
-    "filename": {
-      "minLength": 1,
-      "type": "string"
-    },
-    "mimeType": {
-      "minLength": 1,
-      "type": "string"
-    }
-  },
-  "required": [
-    "filename",
-    "mimeType",
-    "content"
-  ],
-  "type": "object"
-}

removedInput schema / properties / attachments / type
```
Removed value: -"array"
```
removedInput schema / properties / bcc / $ref
```
Removed value: -"#/properties/to"
```

addedInput schema / properties / bcc / anyOf

Added value: +[
+  {
+    "$ref": "#/properties/to/anyOf/0"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / properties / bodyHtml / type

Previous value: -"string"New value: +[
+  "string",
+  "null"
+]

changedInput schema / properties / bodyText / type

Previous value: -"string"New value: +[
+  "string",
+  "null"
+]

removedInput schema / properties / cc / $ref
```
Removed value: -"#/properties/to"
```

addedInput schema / properties / cc / anyOf

Added value: +[
+  {
+    "$ref": "#/properties/to/anyOf/0"
+  },
+  {
+    "type": "null"
+  }
+]

addedInput schema / properties / draftId / anyOf

Added value: +[
+  {
+    "minLength": 1,
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

removedInput schema / properties / draftId / minLength
```
Removed value: -1
```
removedInput schema / properties / draftId / type
```
Removed value: -"string"
```

addedInput schema / properties / from / anyOf

Added value: +[
+  {
+    "format": "email",
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

removedInput schema / properties / from / format
```
Removed value: -"email"
```
removedInput schema / properties / from / type
```
Removed value: -"string"
```

changedInput schema / properties / replyAll / type

Previous value: -"boolean"New value: +[
+  "boolean",
+  "null"
+]

removedInput schema / properties / replyToMessageId / $ref
```
Removed value: -"#/properties/draftId"
```

addedInput schema / properties / replyToMessageId / anyOf

Added value: +[
+  {
+    "$ref": "#/properties/draftId/anyOf/0"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / properties / subject / type

Previous value: -"string"New value: +[
+  "string",
+  "null"
+]

addedInput schema / properties / to / anyOf

Added value: +[
+  {
+    "description": "Recipients, each \"Name <a@x.com>\" or \"a@x.com\"",
+    "items": {
+      "minLength": 1,
+      "type": "string"
+    },
+    "type": "array"
+  },
+  {
+    "type": "null"
+  }
+]

removedInput schema / properties / to / items

Removed value: -{
-  "minLength": 1,
-  "type": "string"
-}

removedInput schema / properties / to / type
```
Removed value: -"array"
```

Changed1 schema field changedv0.11.1Oct 1, 2026
- removedOutput schema / $schema
```
Removed value: -"http://json-schema.org/draft-07/schema#"
```
Addedv0.11.0Sep 26, 2026

TDQS

A3.5/5.0

Behavior3/5

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the no-side-effect profile is covered. The description adds value with 'resolved' (implying address resolution / recipient computation), but it never says whether invalid input produces errors or warnings, which is the core behavioral question for a preview tool.

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?

A single front-loaded sentence with no filler. The most important constraint ('without sending mail') is placed at the end of a compact clause and nothing is wasted.

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

Completeness3/5

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

With 12 optional parameters, an output schema, and strong annotations, the definition is not wrong but is thin. It omits whether the preview reports validation failures or diffs against an existing draft, which is what an agent actually needs to decide to call it.

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 83%, so parameters are largely self-documenting. The description enumerates the resolved fields (sender, recipients, subject, attachments), which maps loosely onto from/to/cc/bcc/subject/attachments, but adds nothing about draftId, replyToMessageId, replyAll, or accountId. Baseline 3 applies.

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?

Names a specific verb and resource set ('Show the resolved sender, recipients, subject and attachments') and clearly distinguishes itself from the sibling send_email with 'without sending mail'. It does not name the alternative explicitly, but the non-sending preview scope is unmistakable.

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?

Usage is only implied: the phrase 'without sending mail' suggests a dry-run before send_email, but the description never says when to prefer this over just calling send_email, nor whether it should always be called first. No exclusions or preconditions are stated.

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