Email for products that ship with agents

A painted alpine valley at dusk, a river winding toward the mountains

Send a welcome email to everyone who signed up today, from Mara, with a link to the quickstart.

Ask Herald to send…

From Mara at Herald · To 128 people

Welcome to Herald

Your first send is three lines of code away.

Queued 0.2s
Sent 1.1s
Delivered 1.9s

Send API

One POST to send. Templates, attachments, idempotency keys, and a delivery event for every message.

Docs
MCP server

Give your agent tools to send, draft campaigns, manage contacts, and read delivery stats.

Docs
Agent skill

A SKILL.md your coding agent reads once and gets Herald right on the first try.

Docs

3,417,905
Sent, past 7 days: 98.61%
Delivery rate: 1.42s
Time to inbox: 0.87%
Bounce rate

Sent by teams of one and teams of one thousand

#01 – Transactional mail

Codes, receipts, and alerts your users can count on.

One POST, or point your SMTP client at us. Templates, attachments, tags, and an idempotency key so a retried request never sends twice.
Typed clients for Node, Python, PHP, Go, Ruby, and Rust — with the same names as the API, so the docs and the autocomplete agree.
Point an address at Herald and receive every reply as structured JSON: parsed body, attachments, headers, and a verified sender.
A signed event for every delivery, open, click, bounce, and complaint, retried with backoff until you return a 200.

Send a message

curl https://api.herald.dev/v1/send \
  -H "Authorization: Bearer $HERALD_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "Mara <mara@herald.dev>",
    "to": "sam@acme.com",
    "subject": "Welcome to Herald",
    "template": "welcome",
    "data": { "name": "Sam" }
  }'

import { Herald } from 'herald';

const herald = new Herald(process.env.HERALD_KEY);

await herald.send({
  from: 'Mara <mara@herald.dev>',
  to: 'sam@acme.com',
  subject: 'Welcome to Herald',
  template: 'welcome',
  data: { name: 'Sam' },
});

from herald import Herald

herald = Herald(os.environ["HERALD_KEY"])

herald.send(
    from_="Mara <mara@herald.dev>",
    to="sam@acme.com",
    subject="Welcome to Herald",
    template="welcome",
    data={"name": "Sam"},
)

$herald = new Herald\Client(getenv('HERALD_KEY'));

$herald->send([
    'from' => 'Mara <mara@herald.dev>',
    'to' => 'sam@acme.com',
    'subject' => 'Welcome to Herald',
    'template' => 'welcome',
    'data' => ['name' => 'Sam'],
]);

client := herald.New(os.Getenv("HERALD_KEY"))

_, err := client.Send(ctx, herald.Message{
    From:     "Mara <mara@herald.dev>",
    To:       "sam@acme.com",
    Subject:  "Welcome to Herald",
    Template: "welcome",
    Data:     map[string]any{"name": "Sam"},
})

herald = Herald::Client.new(ENV["HERALD_KEY"])

herald.send(
  from: "Mara <mara@herald.dev>",
  to: "sam@acme.com",
  subject: "Welcome to Herald",
  template: "welcome",
  data: { name: "Sam" }
)

Send a message

curl https://api.herald.dev/v1/send \
  -H "Authorization: Bearer $HERALD_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "Mara <mara@herald.dev>",
    "to": "sam@acme.com",
    "subject": "Welcome to Herald",
    "template": "welcome",
    "data": { "name": "Sam" }
  }'

import { Herald } from 'herald';

const herald = new Herald(process.env.HERALD_KEY);

await herald.send({
  from: 'Mara <mara@herald.dev>',
  to: 'sam@acme.com',
  subject: 'Welcome to Herald',
  template: 'welcome',
  data: { name: 'Sam' },
});

from herald import Herald

herald = Herald(os.environ["HERALD_KEY"])

herald.send(
    from_="Mara <mara@herald.dev>",
    to="sam@acme.com",
    subject="Welcome to Herald",
    template="welcome",
    data={"name": "Sam"},
)

$herald = new Herald\Client(getenv('HERALD_KEY'));

$herald->send([
    'from' => 'Mara <mara@herald.dev>',
    'to' => 'sam@acme.com',
    'subject' => 'Welcome to Herald',
    'template' => 'welcome',
    'data' => ['name' => 'Sam'],
]);

client := herald.New(os.Getenv("HERALD_KEY"))

_, err := client.Send(ctx, herald.Message{
    From:     "Mara <mara@herald.dev>",
    To:       "sam@acme.com",
    Subject:  "Welcome to Herald",
    Template: "welcome",
    Data:     map[string]any{"name": "Sam"},
})

herald = Herald::Client.new(ENV["HERALD_KEY"])

herald.send(
  from: "Mara <mara@herald.dev>",
  to: "sam@acme.com",
  subject: "Welcome to Herald",
  template: "welcome",
  data: { name: "Sam" }
)

Inbound · parsed

from: sam@acme.com
subject: Re: Your invoice for March
reply: Paid this morning, thanks.
attachments: []
in_reply_to: msg_8f2k
auth: SPF · DKIM · DMARC

Delivery log

sam@acme.com Delivered 1.1s
j.lee@northwind.io Delivered 0.9s
riley@marsh.studio Delivered 1.4s
ops@frostline.io Deferred 12.0s
old-address@example.org Bounced 0.3s
hello@looply.app Delivered 1.2s
team@orbital.dev Delivered 1.0s

All about transactional mail

#02 – Broadcasts

Newsletters and launches that land in the inbox, not the tab.

Write a broadcast, pick a segment, schedule it. Newsletters, launches, and the occasional apology all go out the same way.
Herald ramps a new domain over three weeks so mailbox providers learn to trust it before you send your first big list.
Filter contacts by property, event, or engagement, and the segment updates itself as people qualify or fall out.
Write in markdown, preview in every major client, and ship a message that renders the same in Gmail and Outlook.

Campaigns

Broadcasts to a segment of your contacts.

Sending 24 Mar, 2026 · 10:24

Inbound is live

Subject: Replies now arrive as JSON
Sent 20 Mar, 2026 · 09:40

March notes

Subject: What we shipped, and one thing we broke
Sent 12 Mar, 2026 · 08:15

Warmup week three

Subject: Your domain is ready for the big list
Draft Not scheduled

Pricing update

Subject: A smaller bill for most of you

Domain warmup

1
3
5
7
9
11
13
14

Day 14 of 21 · cap doubles while bounces stay low

Segment · Active on Pro

Where plan is pro
And last_seen within 30 days
And emails_opened at least 3

2,410 contacts match right now

Editor · March notes

# What we shipped

Inbound mail is live. Point an address at Herald and every reply arrives as JSON.

[Read the changelog](/changelog)

What we shipped

Inbound mail is live. Point an address at Herald and every reply arrives as JSON.

Read the changelog

All about broadcasts

#03 – Automations

Sequences that send themselves, from signup to renewal.

Welcome series, onboarding nudges, and win-back campaigns that run themselves once a contact enters them.
Start a sequence from a signup, a property change, or an event your product sends, and stop it the moment they convert.
Opens, clicks, and conversions per step, so you can see which message does the work and which one gets skipped.

Trigger

Contact is added to New signups
Welcome to Herald From Mara <mara@herald.dev>
Wait for 2 days
Your first send, step by step Skipped if they have already sent
Wait for 5 days
Sequence ends

When every email has gone out, or the moment the contact upgrades.

Triggers

contact.created Starts Welcome series
plan.changed → pro Starts Getting the most from Pro
invoice.overdue Starts Payment reminders
contact.inactive_30d Starts Win-back

Analytics · last 30 days

Delivered 98.6% +0.4
Opened 61.2% +3.1
Clicked 18.7% +1.9
Upgraded 4.3% +0.8

All about automations

Workspaces

Every product, one bill.

Create a workspace for each product, client, or environment you run, each with its own domains, contacts, templates, and API keys — and one invoice at the end of the month.

Painted moorland hills at dawn with a chalk path over the ridge

Acme

Acme mail.acme.com
Frostline frostline.io
Staging staging.acme.com
New workspace

Agent integrations

Works with the agent you already use.

We moved 190,000 users off a contact-priced plan in an afternoon. The bill went down by two thirds and nobody noticed the switch.

Sam Okafor Founder, Orbital
The migration took a morning. The team answered every question the same day, and the product does what the bigger names do without the bigger invoice.

Jordan Lee Engineering lead, Pine Labs
Our agents send receipts and alerts on their own now. The MCP tools and the skill file mean they get the send right without a human reviewing every call.

Riley Marsh CTO, Looply

Ask around.

See what your favourite model says about Herald, then decide for yourself.

Send the message. Skip the plumbing.

Send API