I'm currently building an app that automates the logistics of tech conferences. It generates certificates of participation for both attendees and speakers and also takes care of sending invitations to prospective presenters. Since it emails multiple recipients, the question arises: in a development environment, how do you test email sending without using real accounts?
In this tutorial, you'll learn how to configure a fake SMTP server and run email tests for Python apps.
Configure a Local SMTP Server
I'm using Mailpit, an Open Source email testing tool. It can be installed following the instructions in the Installation section of the official repository, or by using Docker.
To ensure your data survives a container restart, run the Docker container with a volume to enable persistence:
docker run -d \
--name mailpit \
-p 1025:1025 \
-p 8025:8025 \
-v $(pwd)/mailpit-data:/data \
axllent/mailpit
The server listens for SMTP traffic on port 1025, while the web-based dashboard is accessible via port 8025.
Running Tests for Python
Let's create a script to test our email logic. The script will perform the following tasks:
- Create a list of random names and emails using Faker
- Construct MIME headers (From, To, Subject)
- Render the HTML body
- Establish and SMTP connection and transmit the data
- Create a recipient list.
First, we generate a list of participants.
from faker import Faker
fake = Faker('en_US')
if __name__ == "__main__":
participants = [(fake.name(), fake.ascii_company_email()) for _ in range(10)]
The generated data will look like this:
Name | Email
-------------------------------------------------------
Jessica Powell | [email protected]
Chelsey Glover | [email protected]
Sheryl Williams | [email protected]
Paula Boyd | [email protected]
Maxwell Kelly | [email protected]
Carl Morrow | [email protected]
David Webb | [email protected]
Tyler Wolfe | [email protected]
Joshua Medina | [email protected]
Mrs. Donna Butler | [email protected]
- Construct MIME Headers
We use Python's built-inemail.mimelibrary to structure the message.
...
from email.mime.multipart import MIMEMultipart
def send_simple_email(recipient_email, recipient_name):
SENDER_EMAIL = "[email protected]"
msg = MIMEMultipart()
msg['From'] = SENDER_EMAIL
msg['To'] = recipient_email
msg['Subject'] = f"Invitation: {recipient_name}"
- Render the HTML body
We attach the HTML content to our MIME message.
...
from email.mime.text import MIMEText
def send_simple_email(recipient_email, recipient_name):
...
html_body = f"""
<html>
<body style="font-family: sans-serif;">
<h2 style="color: #2c3e50;">Hello, {recipient_name}!</h2>
<p>You are formally invited to participate as a speaker at our next event.</p>
<p>This is a test email captured locally by <strong>Mailpit</strong>.</p>
</body>
</html>
"""
msg.attach(MIMEText(html_body, 'html'))
- Establish SMTP connection and transmit email data
Finally, we connect to the local Mailpit server and send the message.
import smtplib
...
def send_simple_email(recipient_email, recipient_name):
...
SMTP_SERVER = "localhost"
SMTP_PORT = 1025
try:
with smtplib.SMTP(SMTP_SERVER, SMTP_PORT) as server:
server.send_message(msg)
return True
except Exception as e:
print(f"❌ Error: {e}")
return False
if __name__ == "__main__":
...
print(f"\n📧 Starting email delivery to {len(participants)} recipients...")
for name, email in participants:
if send_simple_email(email, name):
print(f" ✅ Captured: {email}")
print("\n🚀 Check your emails at: http://localhost:8025")
The Complete Script
Here is the full implementation:
import smtplib
from faker import Faker
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
fake = Faker('en_US')
def send_simple_email(recipient_email, recipient_name):
SENDER_EMAIL = "[email protected]"
msg = MIMEMultipart()
msg['From'] = SENDER_EMAIL
msg['To'] = recipient_email
msg['Subject'] = f"Invitation: {recipient_name}"
html_body = f"""
<html>
<body style="font-family: sans-serif;">
<h2 style="color: #2c3e50;">Hello, {recipient_name}!</h2>
<p>You are formally invited to participate as a speaker at our next event.</p>
<p>This is a test email captured locally by <strong>Mailpit</strong>.</p>
</body>
</html>
"""
msg.attach(MIMEText(html_body, 'html'))
SMTP_SERVER = "localhost"
SMTP_PORT = 1025
try:
with smtplib.SMTP(SMTP_SERVER, SMTP_PORT) as server:
server.send_message(msg)
return True
except Exception as e:
print(f"❌ Error: {e}")
return False
if __name__ == "__main__":
participants = [(fake.name(), fake.ascii_company_email()) for _ in range(10)]
print(f"\n📧 Starting email delivery to {len(participants)} recipients...")
for name, email in participants:
if send_simple_email(email, name):
print(f" ✅ Sent: {email}")
print("\n🚀 Check your emails at: http://localhost:8025")
Viewing the Results
After running the script, navigate to http://localhost:8025 in your browser. You will find the Mailpit dashboard with an inbox containing all the successfully intercepted test emails.
Now you can safely test email features before deploying to production.
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