---
title: Sending email | SendHQ Docs
description: Send transactional messages, batches, replies, attachments, and hosted templates safely.
canonical: https://sendhq.cc/docs/sending
last-updated: 2026-09-07
---
# Sending email

Send transactional messages, batches, replies, attachments, and hosted templates safely.

## Message content

Provide a `from` identity on a verified workspace domain, at least one `to` recipient, and HTML, text, or one published hosted template. A raw-content send may omit `subject`, which produces an empty subject. SendHQ generates a text alternative from HTML when needed, but an authored alternative is more reliable.

## Recipients and credits

A message may contain at most 100 combined To, Cc, and Bcc destinations. Each destination consumes one recipient-delivery credit. Duplicate normalized recipient addresses are checked once for suppressions, while every destination still counts toward message limits.

## Safe retries

Send a stable `Idempotency-Key` of at most 200 characters on single and batch submissions. Reusing a key with the identical JSON payload replays the stored response and adds `Idempotent-Replayed: true`. Changing any recipient, content, header, or template data under the same key returns `409`; a concurrent request with that key also returns `409` while the first is pending.

## Batch sending

`POST /emails/batch` accepts up to 100 message objects and returns a result for every position. Use separate message objects for personalized template data rather than sending one personalized template to multiple recipients.

## Replies and threads

Set `reply_to_email_id` when replying. SendHQ derives Message-ID, In-Reply-To, References, and the existing thread ID. Retrieve the complete conversation with `GET /threads/:id`.

## Status model

**queued** Stored before provider submission **sent** Accepted by the provider **delivered** Recipient server accepted delivery **bounced** Permanent delivery failure **complained** Recipient reported spam **failed** Provider submission failed