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Transactional emails are automated messages sent to individual users in response to specific actions, such as password resets, order confirmations, welcome emails, and account notifications. This guide will walk you through setting up transactional email sending in Sender.

Before you begin, make sure you have verified your domain and its DNS parameters (SPF, DKIM and DMARC) in your Sender account. Click here for detailed instructions on how to do that. 

Once your domain is verified, you can start sending transactional emails using either the API or SMTP relay.

Sending Emails with API

API allows you to send transactional emails programmatically. We support multiple programming languages and provide ready-to-use code examples.

Sender’s API documentation can be found here.

API documentation for sending an email campaign without a template can be found here.

Getting Started with API

1. Navigate to your Setup instructions page in Sender
2. Verify that your sending domain is authenticated
3. Create an API token (if you haven’t already)
4. Choose your preferred integration method from the available options:

• cURL – for quick testing via command line
• Laravel – PHP framework with built-in mail support
• PHP – native PHP implementation
• Node.js – JavaScript/Node.js integration
• SMTP – standard SMTP relay option

API Integration Examples

cURL Integration

The quickest way to test sending emails is using cURL. Copy the following command into your terminal:

curl "https://api.sender.net/v2/message/send" \
-X POST \
-H "Accept: application/json" \
-H "Content-Type: application/json" \
-H "Authorization: Bearer YOUR_TOKEN_HERE" \
-d '{
"from": {
"email": "[email protected]",
"name": "Gabrielle"
},
"to": {
"email": "[email protected]",
"name": "John"
},
"subject": "Hello from Sender!",
"html": "Hello, and happy sending!"
}'

Important: Replace YOUR_TOKEN_HERE  with your actual API token, and update the FROM and TO email addresses. The FROM email address must match your verified domain.

Once you send your email, you can check the status of your message in Logs.

Logs can be filtered by event types:

• Emails sent
• Opens
• Clicks
• Bounces
• Unsubscribes
• Spam reports

You can also search for a log by email address, the sender’s domain and campaign name.

You can choose the date range for the logs that you are interested in.

Laravel Integration

Sender provides a Laravel mail transport package for seamless integration with Laravel’s Mail facade:

1. Install the SDK (auto-discovery registers SenderServiceProvider):

composer require sendernet/sender-transactional-php

2. Run the installer for guided setup:

php artisan sender:install

3. Configure environment variables:

SENDER_API_KEY=your_api_key
MAIL_MAILER=sender

4. Use Laravel’s mailing features as usual. Any SenderNetRequestException raised by the SDK is converted into Symfony\Component\Mailer\Exception\TransportException with the original message preserved.

PHP Integration

For standard PHP applications, install the recommended HTTP client and SDK:

Install the HTTP client and factories:

composer require php-http/guzzle7-adapter nyholm/psr7

Install the SDK:

composer require sendernet/sender-transactional-php

Example usage:

use SenderNet\SenderNet;
use SenderNet\Helpers\Builder\EmailParams;
use SenderNet\Helpers\Builder\Recipient;

$sender = new SenderNet(['api_key' => getenv('SENDER_API_KEY')]);

$emailParams = (new EmailParams())
    ->setFrom('[email protected]')
    ->setFromName('Gabrielle')
    ->setRecipients([new Recipient('[email protected]', 'User')])
    ->setSubject('Welcome')
    ->setText('Thanks for signing up\!');

$response = $sender->email->send($emailParams);

Sending Emails with SMTP

SMTP (Simple Mail Transfer Protocol) is a standard protocol for sending emails. Many applications and content management systems support SMTP configuration.

Setting Up SMTP

1. Navigate to your Setup instructions page in Sender
2. Select the SMTP tab
3. Click Create SMTP user to generate your credentials

You’ll receive the following information:

• Server: smtp.sender.net
• Ports: 25, 2525, or 587
• Authentication: PLAIN or LOGIN over TLS
• Username: (automatically generated, e.g., Gabrielle_e736w1)
• Password: (provided when creating the user; safe it as it will only be shown once)

Configuring SMTP in Your Application

Enter the following settings in your application or CMS:

• SMTP Host/Server: smtp.sender.net
• Port: 25, 2525, or 587 (choose based on your server configuration)
• Encryption: TLS or STARTTLS
• Username: Your generated SMTP username
• Password: Your SMTP password

Important: The from email address must match your verified domain.

Managing SMTP Users

From the SMTP Users section, you can:

• Edit user settings
• Regenerate password if credentials are compromised or you lost the password
• Delete users you no longer need

JavaScript/Node.js Integration

Here’s a complete example of sending a transactional email:

var axios = require('axios');

Configuration Parameters

URL Structure: Replace CAMPAIGN_ID with your actual campaign ID from your Sender account.

Authentication: Replace PLACE_YOUR_API_TOKEN_HERE with your API token, which you can find in your Sender account settings.

Request Body:

• to: Recipient information including email address and name
• variables: Custom variables that can be used in your email template (like firstname, lastname)
• text: The email content or a trigger for your template

All other available parameters can be found at api.sender.net.

API Features and Capabilities

Sending to Multiple Recipients

For individual personalized emails: Make separate API calls for each recipient to ensure personalization and privacy.

For bulk sending: Use Sender’s bulk endpoint to send to multiple recipients efficiently. Note that when multiple recipients are added to the same “to” field, they will be able to see each other’s email addresses.

Adding Attachments

You can attach files to your transactional emails by including file URLs in your API request:

{
  "attachments": {
    "invoice.pdf": "https://yourdomain.com/files/invoice.pdf",
    "receipt.pdf": "https://yourdomain.com/files/receipt.pdf"
  }
}

Attachment requirements:

• Files must be accessible via HTTPS URLs
• Maximum file size: 25MB per attachment
• Supported formats: PDF, Office documents, images, ZIP files, and more

Send Transactional Emails with SMTP via Python

1. Generate your Credentials

1. Navigate to the Transactional Emails section in your Sender dashboard and click on Setup instructions.
2. Select the SMTP tab.
3. Click Add SMTP User to generate a dedicated alphanumeric username (e.g., USER_elRMvr) and password.

2. Input Parameters in Your Application

Enter the following settings exactly within your application framework or environment config:

• SMTP Host/Server: smtp.sender.net
• Port: 587 (Recommended for modern web frameworks with STARTTLS) or 25 / 2525.
• Encryption: TLS / STARTTLS
• Username: Your generated Sender SMTP username.
• Password: Your generated SMTP password.

3. Python Integration Example

4. Common Pitfalls for Python SMTP Users

• The send_message() Header Wrap: Python’s high-level server.send_message() helper automatically formats email headers. If the generated multi-part boundary line is long, Python splits it across multiple lines but often drops the required leading whitespace tab. This triggers a 550 Unable to parse msg. rejection from our inbound servers. Solution: Use outer_msg.as_bytes(policy=email.policy.SMTP) and pass the resulting bytes into server.sendmail() instead.
• Using the SMTP Username as the Sender Address: The alphanumeric SMTP username generated in your dashboard (e.g., USER_elRMvr) is an API credential, not an email address. Placing a bare username string inside your From: or Message-ID fields will break protocol parser validation. Solution: Always formulate fully qualified addresses ([email protected]) inside your message header blocks.
• Flawed MIME Hierarchy Nesting: When sending text alongside attachments, failing to nest your objects correctly causes modern email clients to display raw payload code or drop files entirely. Solution: Maintain an outer multipart/mixed structure for the attachment layout and embed an inner multipart/alternative structure for your plaintext and HTML body options.

5. Method 1 Frequently Asked Questions (FAQs)

Q: Why does my Python script hang or experience socket connection timeouts?
A: Most cloud computing providers (such as AWS EC2, DigitalOcean, or Linode) and consumer ISPs block outbound traffic on Port 25 to mitigate spam. Ensure your application configuration targets Port 587 with STARTTLS enabled.

Q: Can I use Port 465 with the provided code snippet?
A: No. Port 465 is not supported, as it’s not RFC compliant. The provided code snippet uses Port 587, which initializes an unencrypted connection and upgrades it safely via opportunistic TLS.

Q: How do I handle file attachments that contain international characters or non-ASCII names?
A: Standard ASCII strings cannot natively support international character variants in email headers. If you attempt to pass a filename with special characters directly into add_header, it will corrupt your message formatting. To fix this, explicitly encode the filename parameters using a UTF-8 tuple inside the attachment block:

attachment.add_header(
    "Content-Disposition", 
    "attachment", 
    filename=('utf-8', '', 'invoice.pdf')
)

Using Transactional Email Templates

Sender allows you to create and use email templates with your transactional emails for consistent branding and easier management.

API documentation for sending a transactional email with a template can be found here.

Creating a Template

1. Navigate to the Transactional email overview page
2. Create or select an existing template
3. Complete the Settings, Design, and API steps
4. In the API step, select your preferred programming language (JavaScript, PHP, or Python)

Template API Examples

Each template has a unique campaign ID that you’ll use in your API calls. You can find this ID in the API example section of your template.

The API example section provides language-specific code examples with your template ID already included:

• JavaScript – Using axios
• PHP – Native PHP implementation
• Python – Using requests library

Important: Replace PLACE_YOUR_API_TOKEN_HERE with your actual API token in the code examples.

Sending a Test Email

Before going live, you can test your template:

1. Go to the Transactional email overview page
2. Enter your email address
3. Click Send to receive a test email

Variables

Personalize your transactional emails using variables and dynamic content to create unique experiences for each recipient.

Using Liquid Tags

Liquid tags allow you to insert dynamic content into your emails. Liquid tags should be enclosed in double curly brackets:

Hello {{firstname}},  Your order {{order_id}} has been confirmed.

When sending via API, pass the personalization data:

{
  "to": {
    "email": "[email protected]",
    "name": "John"
  },
  "subject": "Order Confirmation",
  "html": "Hello {{firstname}}, your order {{order_id}} is confirmed.",
  "variables": {
    "firstname": "John",
    "order_id": "12345"
  }
}

Liquid tag rules:

• Must be enclosed in double curly brackets: {{variable}}
• May contain alphanumeric characters and underscores
• Must not start with a number or underscore
• Are case-sensitive: {{VAR}} is different from {{var}}

Conditional Content

Show different content based on conditions, e.g.:

{% if subscription_level == 'premium' %} You’re enjoying all premium features 🎉 {% else %} Upgrade your subscription to access premium features. {% endif %}

Common Issues and Solutions

Email not sending:

• Verify that your from email address matches your verified domain,
• Check that your API token or SMTP credentials are valid and active,
• Ensure you’re providing either HTML content, text content, or a template ID,
• Confirm your request format follows the API documentation exactly,
• Check that all required fields are included in your request.

Authentication errors:

• Confirm your API token is correct and hasn’t been regenerated
• Esure the API token has not expired (use “Forever” for transactional emails)
• For SMTP, verify your username and password are entered correctly and without extra spaces
• Check that your account has sending permissions and is not suspended

Recipient not receiving emails:

• Check if the subscriber status is active (not bounced, unsubscribed, or reported spam)
• Verify the recipient’s email address is valid and has no typos
• Look for bounce or spam complaint notifications in your activity log
• Check if your domain’s sending reputation is healthy
• Ensure SPF, DKIM, and DMARC records for your domain are properly configured and verified

Template issues:

• Verify your Campaign ID is correct in the API call
• Check that all liquid tags are properly closed with matching brackets
• Test liquid tag syntax with sample data before sending live
• Ensure custom fields referenced in liquid tags exist in your subscriber data, if not – set up default values.

API Error Codes

Understanding error codes helps you quickly identify and fix issues:

Code	Meaning	Common Solution
400	Bad request	Review your request format and ensure all JSON is valid
401	Unauthorized	Verify your API token is correct and properly formatted
403	Forbidden	Check your account permissions and sending limits
404	Not found	Verify the endpoint URL and Campaign ID are correct
422	Validation error	Review the error message for specific field issues
429	Too many requests	Reduce your request rate or implement exponential backoff
500	Server error	Retry your request after a brief delay

Common 422 Validation Errors

Error Message	What It Means	Solution
“From email must be verified”	The sender address doesn’t match your verified domain	Use an email address from your verified domain
“Recipient email required”	No recipient specified	Include at least one recipient in the “to” field
“Invalid email format”	Email address is malformed	Check for typos and proper email format ([email protected])
“Content required”	No email content provided	Include either “html” or “text” field in your request
“Campaign not found”	Invalid Campaign ID	Verify the Campaign ID from your template settings
“Rate limit exceeded”	Too many requests sent	Implement rate limiting in your application

Email status meaning

Track your email delivery with these status indicators:

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If you got stuck on a specific task or can’t find a way to execute a particular job, contact our support team via LiveChat or [email protected] – we’re here to help 24/7.

We are excited to announce that Transactional Emails are now available across all Sender plans—from Free to Enterprise.

Whether you need to send password resets, order confirmations, or shipping notifications, you can now manage everything within the same ecosystem you use for your marketing campaigns. We’ve designed our transactional infrastructure to ensure high-speed delivery, robust security, and developer-friendly integration.

Here is an overview of the features available and a breakdown of plan-specific limits.

What features are included?

Our transactional email suite is built to make your life easier, whether you are a developer setting up the API or a marketer analyzing delivery reports.

• API & SMTP: Choose the setup that fits your workflow. Hit our REST endpoint or use standard SMTP relay.

  
  

• Libraries & Documentation: We provide setup guides to help you get up and running quickly.

  
  

Powerful Content & Personalization

• Dynamic Templates: Manage your transactional templates (like invoices or welcome emails) directly in Sender. You can update copy or design without touching your codebase.

  
  

• Liquid Syntax: easily drop in variables like customer names, order totals, or conditional content based on user data.

  
  

• Attachments: Send PDFs, invoices, or documents up to 10MB. All files are virus-scanned and transferred securely.

  
  

Analytics & Tracking

• Real-time Analytics: Track every step from “send” to “inbox.”

  
  

• Detailed Logs: Search and filter records of every email sent to troubleshoot delivery issues.

  
  

• Webhooks: Get instant notifications when emails are delivered, opened, or clicked to trigger follow-up actions in your own systems.

  
  

Security & Deliverability

• High-Priority Sending: We utilize a low-latency send path and smart queuing to ensure time-sensitive emails (like OTPs) land instantly.

  
  

• Built-in Authentication: We handle SPF, DKIM, and DMARC support to protect your domain reputation.

  
  

• Suppression Management: Automatic handling of bounces and complaints to keep your list clean.

  
  

Feature Availability by Plan

While transactional email capability is unlocked for all users, specific limits regarding data retention, team access, and infrastructure vary by plan tier.

Features Available on ALL Plans

Every plan (Free, Standard, Professional, Enterprise, and Prepaid credits) includes:

• Full access to API and SMTP.

  
  

• Dynamic Templates and Liquid syntax.

  
  

• Real-time analytics and engagement tracking.

  
  

• Standard Domain Authentication (SPF/DKIM/DMARC).

  
  

• Unlimited Custom Sending Domains.

  
  

• TLS Encryption and GDPR Compliance.

  
  

Plan-Specific Limits

Below is a breakdown of how the plans differ regarding advanced features and retention limits:

Free Plan

• Webhooks: 1 Event Webhook.

  
  

• Teammate Permissions: 1 User.

  
  

• Log & Bounce Retention: 1 Day.

  
  

• Support: Standard knowledge center access.

  
  

Standard & Prepaid Credit Plans

• Webhooks: 5 Event Webhooks.

  
  

• Teammate Permissions: 3 Users.

  
  

• Log & Bounce Retention: 1 Day.

  
  

• Support: Access to deliverability support.

  
  

Professional Plan

• Webhooks: Unlimited.

  
  

• Dedicated IP: 1 Included (Pooled IP also available).

  
  

• Teammate Permissions: 10 Users.

  
  

• Log & Bounce Retention: 5 Days.

  
  

• Support: Priority deliverability support.

  
  

Enterprise Plan

• Webhooks: Unlimited.

  
  

• Dedicated IP: 1 Included.

  
  

• Teammate Permissions: Unlimited.

  
  

• Log & Bounce Retention: 30 Days.

  
  

• Security: Single Sign-On (SSO) included.

  
  

Ready to get started?

To begin sending transactional emails, navigate to the Transactional emails section in your dashboard to generate your API keys or configure your SMTP settings.

That’s it!

If you got stuck on a specific task or can’t find a way to execute a particular job, contact our support team via LiveChat or [email protected] we’re here to help 24/7.