Send your first email

Test sending works today, even before DNS verification, and test emails are never delivered. Live sending is limited during the public preview. Create a free account, then follow these four steps.

Add a domain

Add your sending domain. DNS can stay pending. A test key can send from that domain before it is verified. Publish the DNS records returned by the API when you want live delivery.

Create a test key

Create a sending key in test mode and keep it on your server. Set SENDTIER_API_KEY to that key (st_test_…). Never expose it in browser code or commit it to source control. A test key does not deliver mail.

Send a test email

Use one of the HTTP samples. Replace the sender with an address on the domain you added and the recipient with your own address.

Send POST https://api.sendtier.com/emails with API-Version: 2026-10-01 and Authorization: Bearer st_test_…. The to field is an array.

A successful request returns 202 with an email ID and queued status. Queued means accepted. The test email is not delivered. Read its events in the dashboard, or with a full-access key through GET /emails/{id}. On a live send, a bounce event includes the receiving server’s reply when Amazon SES reports one.

Live sending requirements

Live sending requires a verified domain and an st_live_… key, and remains limited during the public preview. A live key returns 422 domain_not_verified until the domain is verified. Register a webhook endpoint for signed event payloads, and check suppressions in the dashboard before retrying a failed address.

For POST /emails, include an Idempotency-Key on the first request and reuse it with the same request body when retrying.

curl --request POST https://api.sendtier.com/emails \
  --header "Authorization: Bearer $SENDTIER_API_KEY" \
  --header 'API-Version: 2026-10-01' \
  --header 'Content-Type: application/json' \
  --data '{
    "from": "Example <hello@mail.example.com>",
    "to": ["user@example.com"],
    "subject": "Your first email",
    "text": "Hello from Sendtier."
  }'

const response = await fetch('https://api.sendtier.com/emails', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${process.env.SENDTIER_API_KEY}`,
    'API-Version': '2026-10-01',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    from: 'Example <hello@mail.example.com>',
    to: ['user@example.com'],
    subject: 'Your first email',
    text: 'Hello from Sendtier.',
  }),
});
console.log(response.status, await response.json());

<?php
$body = json_encode([
    'from' => 'Example <hello@mail.example.com>',
    'to' => ['user@example.com'],
    'subject' => 'Your first email',
    'text' => 'Hello from Sendtier.',
], JSON_THROW_ON_ERROR);
$context = stream_context_create(['http' => [
    'method' => 'POST',
    'header' => [
        'Authorization: Bearer ' . getenv('SENDTIER_API_KEY'),
        'API-Version: 2026-10-01',
        'Content-Type: application/json',
    ],
    'content' => $body,
]]);
echo file_get_contents('https://api.sendtier.com/emails', false, $context);

import json
import os
from urllib.request import Request, urlopen
 
body = json.dumps({
    "from": "Example <hello@mail.example.com>",
    "to": ["user@example.com"],
    "subject": "Your first email",
    "text": "Hello from Sendtier.",
}).encode()
request = Request("https://api.sendtier.com/emails", data=body, method="POST",
    headers={
        "Authorization": "Bearer " + os.environ["SENDTIER_API_KEY"],
        "API-Version": "2026-10-01",
        "Content-Type": "application/json",
    })
with urlopen(request) as response:
    print(response.status, response.read().decode())

package main
 
import (
    "fmt"
    "io"
    "net/http"
    "os"
    "strings"
)
 
func main() {
    body := strings.NewReader(`{"from":"Example <hello@mail.example.com>",
        "to":["user@example.com"],"subject":"Your first email",
        "text":"Hello from Sendtier."}`)
    request, err := http.NewRequest("POST", "https://api.sendtier.com/emails", body)
    if err != nil { fmt.Fprintln(os.Stderr, err); os.Exit(1) }
    request.Header.Set("Authorization", "Bearer " + os.Getenv("SENDTIER_API_KEY"))
    request.Header.Set("API-Version", "2026-10-01")
    request.Header.Set("Content-Type", "application/json")
    response, err := http.DefaultClient.Do(request)
    if err != nil { fmt.Fprintln(os.Stderr, err); os.Exit(1) }
    defer response.Body.Close()
    fmt.Println(response.Status)
    if _, err := io.Copy(os.Stdout, response.Body); err != nil {
        fmt.Fprintln(os.Stderr, err); os.Exit(1)
    }
}

require 'net/http'
require 'json'
 
uri = URI('https://api.sendtier.com/emails')
request = Net::HTTP::Post.new(uri)
request['Authorization'] = 'Bearer ' + ENV.fetch('SENDTIER_API_KEY')
request['API-Version'] = '2026-10-01'
request['Content-Type'] = 'application/json'
request.body = JSON.generate({
  from: 'Example <hello@mail.example.com>',
  to: ['user@example.com'],
  subject: 'Your first email',
  text: 'Hello from Sendtier.',
})
response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) do |http|
  http.request(request)
end
puts response.code, response.body