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Email Sending MCP

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Send Batch Emails

send-batch-emails

Send up to 100 individual transactional emails in one API call, each with customizable to, subject, text, from, and more. Ideal for bulk actions like password resets or receipts, not for broadcast campaigns.

Instructions

Purpose: Send up to 100 transactional emails in one API call. Each item has the same fields as send-email (to, subject, text, from, etc.).

NOT for: Sending one email (use send-email) or the same content to a segment (use create-broadcast + send-broadcast).

When to use: User wants to send many individual emails in bulk (e.g. 50 password resets, 100 receipts). Not for one-to-many broadcasts.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
emailsYesArray of email objects to send (1-100 emails)
idempotencyKeyNoOptional unique key for the whole batch that prevents duplicate batch sends on retries (sent as the Idempotency-Key header). Use the same key when retrying the same batch; use a new key for a different batch. Must be 1-256 characters.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed7 schema fields changedv2.12.0
    • changedInput schema / $schema
      Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"
    • addedInput schema / properties / emails / items / properties / headers
      Added value: +{
+  "additionalProperties": {
+    "type": "string"
+  },
+  "description": "Optional custom email headers as key/value pairs (e.g. {\"List-Unsubscribe\": \"<https://example.com/unsubscribe>\", \"X-Entity-Ref-ID\": \"unique-id\"}).",
+  "propertyNames": {
+    "type": "string"
+  },
+  "type": "object"
+}
    • changedInput schema / properties / emails / items / properties / replyTo / description
      Previous value: -"Reply-to email addresses"New value: +"Reply-to email addresses (e.g. \"support@example.com\" or \"Support Team <support@example.com>\")"
    • removedInput schema / properties / emails / items / properties / replyTo / items / format
      Removed value: -"email"
    • removedInput schema / properties / emails / items / properties / replyTo / items / pattern
      Removed value: -"^(?!\\.)(?!.*\\.\\.)([A-Za-z0-9_'+\\-\\.]*)[A-Za-z0-9_+-]@([A-Za-z0-9][A-Za-z0-9\\-]*\\.)+[A-Za-z]{2,}$"
    • changedInput schema / properties / idempotencyKey / description
      Previous value: -"Optional unique key for the whole batch that prevents duplicate batch sends on retries (sent as the Idempotency-Key header). Use the same key when retrying the same batch; use a new key for a different batch. Max 256 characters."New value: +"Optional unique key for the whole batch that prevents duplicate batch sends on retries (sent as the Idempotency-Key header). Use the same key when retrying the same batch; use a new key for a different batch. Must be 1-256 characters."
    • addedInput schema / properties / idempotencyKey / minLength
      Added value: +1
  2. Changed1 schema field changedv2.11.0
    • addedInput schema / properties / idempotencyKey
      Added value: +{
+  "description": "Optional unique key for the whole batch that prevents duplicate batch sends on retries (sent as the Idempotency-Key header). Use the same key when retrying the same batch; use a new key for a different batch. Max 256 characters.",
+  "maxLength": 256,
+  "type": "string"
+}
  3. First observedv2.10.0

TDQS

A4.2/5.0
Behavior3/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It states the tool sends up to 100 transactional emails and implies batch behavior, but does not disclose potential side effects, partial failure handling, idempotency details, or rate limits. This is adequate but not rich.

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 tightly organized into three labeled sections (Purpose, NOT for, When to use) with no redundant words. Every sentence contributes to understanding the tool's purpose and usage boundaries.

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 schema's rich parameter descriptions and lack of output schema, the description adequately covers purpose, usage, and exclusions. It could be improved by mentioning idempotency or error behavior, but it is largely complete for a batch-email tool.

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?

The schema covers 100% of parameters with descriptions, so the baseline is 3. The description adds a useful pointer that each item has the same fields as send-email, but it does not provide additional semantic detail beyond the schema for the idempotencyKey or email object fields.

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 clearly states the tool's purpose: 'Send up to 100 transactional emails in one API call,' with a specific verb, resource, and scope. It also distinguishes itself from siblings by noting that individual emails should use send-email and broadcasts should use create-broadcast + send-broadcast.

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 includes explicit 'NOT for' and 'When to use' sections, providing clear guidance on when to use this tool versus send-email or create-broadcast + send-broadcast. Examples (50 password resets, 100 receipts) further clarify appropriate use cases.

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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