Twilio Sendgrid Email Send

Overview

Agent safety: Always confirm recipients, subject, and content with the user before sending. Email is irreversible once delivered. Never send email autonomously without explicit user approval — especially for batch sends to multiple recipients.

All email sending goes through POST /v3/mail/send. This endpoint returns 202 Accepted (queued) — NOT 200 OK (delivered). Delivery confirmation comes asynchronously via Event Webhook. See twilio-sendgrid-webhooks.

---

Basic Send

Python

import os, sendgrid
from sendgrid.helpers.mail import Mail

sg = sendgrid.SendGridAPIClient(os.environ["SENDGRID_API_KEY"])
message = Mail(
    from_email="verified@yourdomain.com",
    to_emails="recipient@example.com",
    subject="Order Confirmation",
    html_content="<p>Your order #1234 is confirmed.</p>"
)
response = sg.send(message)
print(f"Status: {response.status_code}")  # 202 = queued

Node.js

const sgMail = require("@sendgrid/mail");
sgMail.setApiKey(process.env.SENDGRID_API_KEY);

const [response] = await sgMail.send({
    to: "recipient@example.com",
    from: "verified@yourdomain.com",
    subject: "Order Confirmation",
    html: "<p>Your order #1234 is confirmed.</p>",
});
console.log(`Status: ${response.statusCode}`); // 202 = queued

---

Personalized Batch Send with Dynamic Templates

Dynamic templates use Handlebars syntax. Template IDs start with d-. Create templates in SendGrid Console > Email API > Dynamic Templates.

Python

from sendgrid.helpers.mail import Mail, To

message = Mail(
    from_email="noreply@yourdomain.com",
    to_emails=[
        To("alice@example.com", dynamic_template_data={"name": "Alice", "order_id": "123"}),
        To("bob@example.com", dynamic_template_data={"name": "Bob", "order_id": "456"}),
    ],
)
message.template_id = "d-xxxxxxxxxxxxxxxxxxxxxxxxxxxx"
sg.send(message)

Node.js

await sgMail.send({
    from: { email: "noreply@yourdomain.com" },
    template_id: "d-xxxxxxxxxxxxxxxxxxxxxxxxxxxx",
    personalizations: [
        { to: [{ email: "alice@example.com" }], dynamic_template_data: { name: "Alice", order_id: "123" } },
        { to: [{ email: "bob@example.com" }], dynamic_template_data: { name: "Bob", order_id: "456" } },
    ],
});

Recipients in the same `to` array within a single personalization can see each other. For private sends, use separate personalizations (one per recipient).

---

Scheduled Sends

Schedule up to 72 hours in advance. Cancellation requires a batch ID assigned before sending.

Python

import time, requests

headers = {"Authorization": f"Bearer {os.environ['SENDGRID_API_KEY']}", "Content-Type": "application/json"}

# Get batch ID first
batch = requests.post("https://api.sendgrid.com/v3/mail/batch", headers=headers).json()

# Include batch_id and send_at in the message
send_at = int(time.time()) + 3600  # Unix SECONDS, not ms

# Cancel if needed (before send_at)
requests.post("https://api.sendgrid.com/v3/user/scheduled_sends",
    headers=headers,
    json={"batch_id": batch["batch_id"], "status": "cancel"})

---

Attachments

Base64-encode files in the attachments array. Total limit: 30MB per request (~22MB before encoding overhead).

import base64
from sendgrid.helpers.mail import Mail, Attachment, FileContent, FileName, FileType, Disposition

with open("invoice.pdf", "rb") as f:
    encoded = base64.b64encode(f.read()).decode()

message = Mail(from_email="billing@yourdomain.com", to_emails="customer@example.com",
               subject="Your Invoice", html_content="<p>Invoice attached.</p>")
message.attachment = Attachment(FileContent(encoded), FileName("invoice.pdf"),
                                FileType("application/pdf"), Disposition("attachment"))
sg.send(message)

---

Categories and Custom Args

Categories tag sends for analytics segmentation (up to 10 per message):

message.category = ["transactional", "order-confirmation"]

Custom Args pass metadata through to Event Webhooks (key-value strings only):

message.custom_args = {"order_id": "1234", "env": "production"}

These appear in webhook event payloads, enabling you to correlate delivery events back to your application data.

---

Sandbox Mode (Testing)

Validates the request without delivering. Returns 200 OK (not 202).

message.mail_settings = {"sandbox_mode": {"enable": True}}
response = sg.send(message)  # 200 = validated, not sent

---

CANNOT

• Cannot send more than 1,000 recipients per API call — Hard limit. Split into multiple requests.
• Cannot schedule sends more than 72 hours in advance — send_at rejects timestamps beyond 72h.
• Cannot cancel a send after processing — Only scheduled messages with a pre-assigned batch ID can be cancelled.
• Cannot use `send_at` with milliseconds — JS Date.now() returns ms. Divide by 1000 or the timestamp is silently rejected (>72h).
• The `subject` field in personalizations is a plain string override — To use dynamic subjects, set Handlebars variables (e.g., {{{subject}}}) in the Dynamic Template's subject field and pass values via dynamic_template_data. The personalizations subject key bypasses the template subject entirely.
• Undefined template variables render as empty strings — No error for typos in dynamic_template_data keys. Silent failures.
• `413 Payload Too Large` returns nginx HTML, not JSON — Exceeding 30MB returns HTML error page. Check Content-Type before parsing.
• Empty `content` when using `template_id` — Omit the content field. If you include both, template_id takes precedence and content is ignored.

Agent usage: When sending email on behalf of a user, always report back what was sent — recipients, subject, and the API response status code. Maintain an application-level audit log for all sends.

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Next Steps

• Account setup and domain auth: twilio-sendgrid-account-setup
• Templates and settings: twilio-sendgrid-email-settings
• Delivery tracking via webhooks: twilio-sendgrid-webhooks
• Manage bounces and unsubscribes: twilio-sendgrid-suppressions