Sovereign transactional email.
Hosted in Canada. Canadian-owned.

// Node 18+ — no dependency, fetch is built in
const res = await fetch('https://zedmail.com/v1/email/send', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${process.env.ZEDMAIL_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    from:    'receipts@boutique.ca',
    to:      'client@example.ca',
    subject: 'Votre reçu',
    html:    '<p>Merci de votre achat.</p>',
    tags:    ['order-4812'],
  }),
});

const { message_id } = await res.json();   // msg_a1b2c3d4e5f6a7b8

<?php
$ch = curl_init('https://zedmail.com/v1/email/send');
curl_setopt_array($ch, [
    CURLOPT_POST           => true,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER     => [
        'Authorization: Bearer ' . getenv('ZEDMAIL_KEY'),
        'Content-Type: application/json',
    ],
    CURLOPT_POSTFIELDS     => json_encode([
        'from'    => 'receipts@boutique.ca',
        'to'      => 'client@example.ca',
        'subject' => 'Votre reçu',
        'html'    => '<p>Merci de votre achat.</p>',
        'tags'    => ['order-4812'],
    ]),
]);

$res = json_decode(curl_exec($ch), true);
echo $res['message_id'];   // msg_a1b2c3d4e5f6a7b8

# .env — Zedmail is a standard SMTP mailer, so Mailables,
# queues and Mail::fake() all keep working unchanged.

MAIL_MAILER=smtp
MAIL_HOST=mail.zedmail.com
MAIL_PORT=465
MAIL_ENCRYPTION=tls
MAIL_USERNAME="${ZEDMAIL_KEY}"
MAIL_PASSWORD="${ZEDMAIL_KEY}"
MAIL_FROM_ADDRESS=receipts@boutique.ca
MAIL_FROM_NAME="Boutique"

# Then, as you already write it:
#   Mail::to($order->email)->send(new ReceiptMail($order));

import os, requests

res = requests.post(
    "https://zedmail.com/v1/email/send",
    headers={"Authorization": f"Bearer {os.environ['ZEDMAIL_KEY']}"},
    json={
        "from":    "receipts@boutique.ca",
        "to":      "client@example.ca",
        "subject": "Votre reçu",
        "html":    "<p>Merci de votre achat.</p>",
        "tags":    ["order-4812"],
    },
    timeout=15,
)
res.raise_for_status()
print(res.json()["message_id"])   # msg_a1b2c3d4e5f6a7b8

body, _ := json.Marshal(map[string]any{
    "from":    "receipts@boutique.ca",
    "to":      "client@example.ca",
    "subject": "Votre reçu",
    "html":    "<p>Merci de votre achat.</p>",
    "tags":    []string{"order-4812"},
})

req, _ := http.NewRequest("POST",
    "https://zedmail.com/v1/email/send", bytes.NewReader(body))
req.Header.Set("Authorization", "Bearer "+os.Getenv("ZEDMAIL_KEY"))
req.Header.Set("Content-Type", "application/json")

res, err := http.DefaultClient.Do(req)
if err != nil {
    return err
}
defer res.Body.Close()

curl https://zedmail.com/v1/email/send \
  -H "Authorization: Bearer $ZEDMAIL_KEY" \
  -H "Content-Type: application/json" \
  -d '{
        "from":    "receipts@boutique.ca",
        "to":      "client@example.ca",
        "subject": "Votre reçu",
        "html":    "<p>Merci de votre achat.</p>",
        "tags":    ["order-4812"]
      }'

# {"message_id":"msg_a1b2c3d4e5f6a7b8","status":"queued"}

Host        mail.zedmail.com
Port        465   (implicit TLS)
            2587  (STARTTLS)
Username    your API key
Password    the same API key

# Never port 25 — we do not use it, so an unblock request
# to your host is wasted effort.

# Test it from a terminal before wiring anything up:
swaks --server mail.zedmail.com:465 --tls-on-connect \
      --auth-user "$ZEDMAIL_KEY" --auth-password "$ZEDMAIL_KEY" \
      --from receipts@boutique.ca --to client@example.ca

<?php
/**
 * wp-content/mu-plugins/zedmail.php
 * A must-use plugin: no plugin to install, nothing to configure in wp-admin,
 * and it cannot be deactivated by accident.
 */
add_action('phpmailer_init', function ($mail) {
    $mail->isSMTP();
    $mail->Host       = 'mail.zedmail.com';
    $mail->Port       = 465;
    $mail->SMTPSecure = 'ssl';
    $mail->SMTPAuth   = true;
    $mail->Username   = ZEDMAIL_KEY;   // define() these in wp-config.php
    $mail->Password   = ZEDMAIL_KEY;
    $mail->setFrom('no-reply@votresite.ca', get_bloginfo('name'));
});