Skip to main content
Glama
Sendmux

Sendmux Email Inbox API + Sending

Official
by Sendmux

Send Email

sending_send_email

Send an outbound email with CC/BCC, HTML/text body, and attachments via uploaded attachment IDs. Include an Idempotency-Key to avoid duplicate sends on retries.

Instructions

Use this to send one outbound email through the sending API. For attachments, call sending_upload_attachment first for local/tiny content or sending_create_attachment_upload for delegated file PUTs, then pass attachments as attachment_id refs. Inline base64 is only for tiny generated content. Include an Idempotency-Key so retries do not create duplicate sends.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
ccNoCC recipients (subject to 50 total To, CC, and BCC recipients)
toYesPrimary recipient
bccNoBCC recipients (subject to 50 total To, CC, and BCC recipients)
fromYesSender address
subjectYesEmail subject line (max 998 chars, RFC 5322)
reply_toNoReply-To address
html_bodyYesHTML email content (max 25MB)
text_bodyNoPlain text alternative (max 25MB)
attachmentsNoFile attachments (max 10). Use attachment_id refs for uploaded files.
return_pathNoEnvelope sender for VERP support
custom_headersNoCustom X-* headers to include in the email
Idempotency-KeyNoOptional client-generated key to make the request idempotent for 24 hours. Replays under the same key return the cached response; a reused key with a different body returns 409 idempotency_conflict.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Behavior4/5

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

The description adds valuable behavioral context beyond the annotations: attachment pre-upload workflow, inline base64 limitation, and idempotency behavior. It does not mention response format or rate limits, but annotations already provide read/write hints and the output schema covers the response. No contradiction with the annotations.

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 four sentences, each earning its place: purpose, attachment workflow, inline base64 constraint, and idempotency guidance. It is front-loaded with the core action and avoids any filler.

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 12 parameters, nested objects, and rich schema, the description covers the main use case (send a single email), the critical attachment workflow, and idempotency. The output schema handles return values, so the description is sufficiently complete without redundancy.

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?

Although schema coverage is 100%, the description adds essential semantics not present in the schema: how attachments should be structured (pre-upload then reference) and the constraint that inline base64 is only for tiny content. It also explains the purpose of the Idempotency-Key, giving the agent deeper understanding of parameter usage.

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 sends one outbound email via the sending API, using the specific verb 'send' and resource 'outbound email'. It distinguishes itself from sibling tools like sending_send_email_batch by emphasizing 'one' email, and from attachment upload tools via the attachment workflow.

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 guides when to use this tool for sending a single email and names alternative tools for related tasks (sending_upload_attachment, sending_create_attachment_upload). It also clarifies when to use inline base64 vs attachment_id refs and advises including an Idempotency-Key, giving concrete operational guidance.

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

Install Server

Other Tools

Latest Blog Posts

MCP directory API

We provide all the information about MCP servers via our MCP API.

curl -X GET 'https://glama.ai/api/mcp/v1/servers/Sendmux/sendmux-sdk'

If you have feedback or need assistance with the MCP directory API, please join our Discord server