How to Send Email in CodeIgniter 4 with SMTP (Step-by-Step Guide)

Sending emails is one of those features that almost every app needs – whether it’s for user sign-ups, password resets, or just notifications. In this tutorial, I’ll walk you through how I set up email sending in CodeIgniter 4 using SMTP with Mailtrap.

We’ll go step by step, starting from scratch, so by the end you’ll have a working project where you can test sending emails right from your local machine.

But before we dive into the tutorial, I’ll quickly cover what SMTP is and why CodeIgniter makes email handling easier, so you have the full context.

What is SMTP?

SMTP stands for Simple Mail Transfer Protocol. It’s the standard protocol that email servers use to send and receive messages across the internet. Instead of relying on PHP’s built-in mail() function (which often fails due to server restrictions), SMTP ensures your emails are delivered more reliably, with proper authentication and encryption.

Why Use CodeIgniter for Email?

CodeIgniter 4 comes with a built-in Email library, which makes handling SMTP a lot easier. You don’t have to worry about writing raw SMTP commands or dealing with complicated configurations.

With just a few settings in your Email.php config file and some simple controller logic, you can send fully functional emails in minutes.

Building the Email Feature in CodeIgniter 4

Now that we understand the basics, let’s roll up our sleeves and set up email sending in CodeIgniter 4 using SMTP.

Prerequisites

Here’s what I have set up on my machine (make sure you’ve got these too):

• Windows 10
• XAMPP Control Panel v3.3.0 (Apache + PHP 8.2)
• Composer 2.8+
• A free Mailtrap account (we’ll use this to safely test emails)

Step 1: Create a New CodeIgniter Project

Fire up the XAMPP Control Panel and start the Apache server.

Open CMD and move into your htdocs folder inside XAMPP:

cd C:\xampp\htdocs

Now let’s create a fresh CodeIgniter project (I’ll name mine ci4-smtp-demo, but you can pick another name if you prefer):

composer create-project codeigniter4/appstarter ci4-smtp-demo

Once installed, test it by visiting:

http://localhost/ci4-smtp-demo/public/

You should see the default CodeIgniter welcome page.

Step 2: Configure .env

In your project folder, rename the file .env.example → .env.

Open it and update these lines:

CI_ENVIRONMENT = development

app.baseURL = 'http://localhost/ci4-smtp-demo/public/'

Step 3: Set Up Mailtrap SMTP

Now we’ll grab SMTP details from Mailtrap.

• Log into your Mailtrap account.
• Go to: Sandboxes → My Sandbox → Integration → SMTP tab.

• Copy the credentials shown there (host, port, username, password).

They’ll look something like this (your username and password will be different):

Host: sandbox.smtp.mailtrap.io

Port: 2525

Username: YOUR_MAILTRAP_USERNAME

Password: YOUR_MAILTRAP_PASSWORD

Open app/Config/Email.php and update the SMTP section like this:

public string $fromEmail  = '[email protected]';     // replace with your "from" email

public string $fromName   = 'My CI4 App';           // replace with your app name

public string $protocol   = 'smtp';

public string $SMTPHost   = 'sandbox.smtp.mailtrap.io';

public string $SMTPUser   = 'YOUR_MAILTRAP_USERNAME';  // replace with your Mailtrap username

public string $SMTPPass   = 'YOUR_MAILTRAP_PASSWORD';  // replace with your Mailtrap password

public int    $SMTPPort   = 2525;                      // you can also use 465 or 587

public string $SMTPCrypto = '';

public string $mailType   = 'html';

public string $charset    = 'utf-8';

Step 4: Create a Mail Controller

Inside app/Controllers/, create a file called MailController.php and add this code:

<?php namespace App\Controllers;

use App\Controllers\BaseController;

class MailController extends BaseController
{
    public function index()
    {
        return view('email_form');
    }

    public function send()
    {
        $request = service('request');
        $to      = $request->getPost('to');                               // recipient email
        $subject = $request->getPost('subject') ?? 'Test Email';
        $message = $request->getPost('message') ?? 'Hello from CodeIgniter 4!';

        $email = \Config\Services::email();
        $email->setTo($to);
        $email->setSubject($subject);
        $email->setMessage($message);

        if ($email->send()) {
            return view('email_success');
        } else {
            echo '<pre>';
            print_r($email->printDebugger(['headers']));
            echo '</pre>';
        }
    }
}

Step 5: Create the Views

We’ll make two simple views inside app/Views/.

email_form.php

<!doctype html>
<html>
<head><title>Send Email</title></head>
<body>
  <h1>Send Email</h1>
  <form method="post" action="<?= site_url('mail/send') ?>">
    <label>Recipient Email:</label><br>
    <input type="email" name="to" placeholder="[email protected]" required><br><br>

    <label>Subject:</label><br>
    <input type="text" name="subject" placeholder="Enter subject"><br><br>

    <label>Message:</label><br>
    <textarea name="message" rows="6" placeholder="Write your message here"></textarea><br><br>

    <button type="submit">Send</button>
  </form>
</body>
</html>

email_success.php

<!doctype html>
<html>
<head><title>Email Sent</title></head>
<body>
  <h1>✅ Email sent successfully!</h1>
  <p>Check your Mailtrap inbox to see the message.</p>
  <a href="<?= site_url('mail') ?>">Send another email</a>
</body>
</html>

Step 6: Add Routes

Open app/Config/Routes.php and add:

$routes->get('mail', 'MailController::index');

$routes->post('mail/send', 'MailController::send');

Test It Out

Now go to:

http://localhost/ci4-smtp-demo/public/mail

Fill in the form, hit Send, and if all goes well you’ll see the success page. Head over to your Mailtrap Sandbox inbox, and your test email will be there waiting.

Wrapping Up!

That’s it — we just built a fully working CodeIgniter 4 email sender using SMTP and Mailtrap.

The great thing about this setup is you can safely test emails locally without worrying about spamming real inboxes. When you’re ready to go live, just swap out the Mailtrap credentials with your production SMTP provider (like Gmail, SendGrid, or Amazon SES).

If you have any questions or confusion, let me know in the comments.

Abdul Rehman

Abdul is a tech-savvy, coffee-fueled, and creatively driven marketer who loves keeping up with the latest software updates and tech gadgets. He's also a skilled technical writer who can explain complex concepts simply for a broad audience. Abdul enjoys sharing his knowledge of the Cloud industry through user manuals, documentation, and blog posts.

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