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Email Sending MCP

by resend

Update Automation

update-automation

Modify automation name, status, or workflow steps to manage email sequences. Disable to stop new runs.

Instructions

Purpose: Update an automation's name, status, or workflow.

When to use:

  • User wants to rename an automation

  • User wants to enable or disable an automation (use status: "disabled" to stop it)

  • User wants to modify the workflow steps

Important:

  • To disable/stop an automation, set status to "disabled". Existing runs will continue to completion.

  • When updating the workflow, provide the complete new workflow — it replaces the existing one.

  • Use get-automation first to see the current workflow before making changes.

The workflow is a JSON object with one key: "steps" — an array of step objects.

Each step has: key (unique string), type, config, and either "next" (string|null) or "branches" (for branching steps). Use keys like: "trigger", "send_email_1", "delay_1", "condition_1", "wait_event_1".

Step types

trigger — starts the automation when an event fires (required, exactly one)

config: { "eventName": "" } Uses "next".

send_email — send an email using a published template

config: { "template": { "id": "", "variables": { "": "" } }, "from": "Name sender@example.com", "subject": "Email subject", "replyTo": "" } "from" and "subject" are resolved from the step config first, then fall back to the template. If neither provides a "from", the email will silently fail to send. If neither provides a "subject", the run will error. Best practice: always set "from" and "subject" on the step config so the automation is self-contained. Use list-domains to find verified domains for "from". "replyTo" and "variables" are optional. Variables can use { "var": "event." } or { "var": "contact." } for dynamic values. Uses "next".

delay — pause the workflow

config: { "duration": "" } Examples: "30 minutes", "1 hour", "2 days", "1 week". Max 30 days. Uses "next".

condition — conditional split based on contact or event data

config: A condition rule object: Single rule: { "type": "rule", "field": "event." or "contact.", "operator": "", "value": } Compound: { "type": "and"|"or", "rules": [, ...] } Operators: eq, neq, gt, gte, lt, lte, contains, starts_with, ends_with, exists, is_empty. exists/is_empty do not require a value. Uses "branches": { "condition_met": "", "condition_not_met": "" }

wait_for_event — pause until a specific event arrives or timeout

config: { "eventName": "", "timeout": "", "filterRule": } For email lifecycle events use "resend:email.<opened|clicked|bounced|delivered|complained|failed|suppressed>". Uses "branches": { "event_received": "", "timeout": "" }

contact_update — update contact fields

config: { "firstName": "", "lastName": "", "unsubscribed": true|false, "properties": { "": "" } } All fields optional. Values can use { "var": "event." } for dynamic data. Uses "next".

contact_delete — remove the contact from the audience

config: {} Uses "next".

add_to_segment — add contact to a segment

config: { "segmentId": "" } Uses "next".

Rules

  1. Every step must be reachable from the trigger via next/branches.

  2. Terminal steps have "next": null (or null branch values).

  3. The workflow must be tree-shaped — no merging branches back together.

Example: Linear drip campaign

{ "steps": [ { "key": "trigger", "type": "trigger", "config": { "eventName": "user.created" }, "next": "send_email_1" }, { "key": "send_email_1", "type": "send_email", "config": { "template": { "id": "tmpl_123" }, "from": "Welcome hello@example.com", "subject": "Welcome!" }, "next": "delay_1" }, { "key": "delay_1", "type": "delay", "config": { "duration": "3 days" }, "next": "send_email_2" }, { "key": "send_email_2", "type": "send_email", "config": { "template": { "id": "tmpl_456" }, "from": "Welcome hello@example.com", "subject": "Getting started" }, "next": null } ] }

Example: Re-engagement with wait_for_event

{ "steps": [ { "key": "trigger", "type": "trigger", "config": { "eventName": "user.created" }, "next": "send_email_1" }, { "key": "send_email_1", "type": "send_email", "config": { "template": { "id": "tmpl_789" }, "from": "Team team@example.com", "subject": "Welcome" }, "next": "wait_event_1" }, { "key": "wait_event_1", "type": "wait_for_event", "config": { "eventName": "resend:email.opened", "timeout": "3 days" }, "branches": { "event_received": null, "timeout": "send_email_2" } }, { "key": "send_email_2", "type": "send_email", "config": { "template": { "id": "tmpl_abc" }, "from": "Team team@example.com", "subject": "Did you miss this?" }, "next": null } ] }

Example: Condition branch

{ "steps": [ { "key": "trigger", "type": "trigger", "config": { "eventName": "trial.ended" }, "next": "condition_1" }, { "key": "condition_1", "type": "condition", "config": { "type": "rule", "field": "event.converted", "operator": "eq", "value": true }, "branches": { "condition_met": "send_email_1", "condition_not_met": "send_email_2" } }, { "key": "send_email_1", "type": "send_email", "config": { "template": { "id": "tmpl_thanks" }, "from": "Team team@example.com", "subject": "Thanks for upgrading!" }, "next": null }, { "key": "send_email_2", "type": "send_email", "config": { "template": { "id": "tmpl_win_back" }, "from": "Team team@example.com", "subject": "We'd love to have you back" }, "next": null } ] }

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
idYesAutomation ID or Resend dashboard URL (e.g. https://resend.com/automations/<id>)
nameNoNew name for the automation.
statusNoNew status. Use "disabled" to stop the automation (prevents new runs).
workflowNoNew workflow definition. Replaces the existing workflow entirely.
Behavior5/5

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

With no annotations, the description fully carries the burden. It explains that setting status to 'disabled' prevents new runs but existing runs finish, that the workflow replaces the existing one entirely, and details the workflow structure and step behaviors.

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?

Despite its length, the description is well-structured with clear headings, examples, and sections. Every sentence adds value, and the format is front-loaded with key information. It is appropriately sized for the tool's complexity.

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 complexity of the workflow object and no output schema, the description is exceptionally complete. It covers all step types, their configuration, constraints, and provides multiple examples, enabling an AI agent to construct valid workflows.

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

Parameters5/5

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

Schema coverage is 100%, but the description adds significant meaning beyond the schema. It explains the status parameter's effect, provides detailed documentation of the workflow structure including all step types, their configs, and examples, which compensates for the complexity of the nested object.

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 explicitly states 'Update an automation's name, status, or workflow,' providing a specific verb and resource. It distinguishes this tool from siblings like create-automation and get-automation by focusing on updating existing automations.

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?

Clear when-to-use scenarios are given: rename, enable/disable (with status), modify workflow. Also includes important notes like using get-automation first and that disabling stops new runs but existing runs continue.

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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