Sending simple emails in Flask - Mini Project: Build & Apply

Sending simple emails

📖 Scenario: You are building a small Flask web app that can send a simple email when a user submits a form. This is useful for contact forms or notifications.

🎯 Goal: Create a Flask app that sets up email configuration, defines a route to send an email, and sends a simple email message.

📋 What You'll Learn

Create a Flask app instance

Configure email server settings using Flask-Mail

Define a route /send-email that sends an email

Send a simple email with subject, sender, recipient, and body

💡 Why This Matters

🌍 Real World

Sending emails is common in web apps for notifications, password resets, and contact forms.

💼 Career

Understanding how to send emails programmatically is a key skill for backend web developers.

1

Set up Flask app and Flask-Mail

Import Flask and Mail from flask_mail. Create a Flask app instance called app. Then create a Mail instance called mail using app.

Flask

from flask import Flask
from flask_mail import Mail

# Create Flask app instance
app = Flask(__name__)

# Create Mail instance
mail = Mail(app)

Hint

Use app = Flask(__name__) to create the app. Then pass app to Mail().

2

Configure email server settings

Add these configuration settings to app.config: MAIL_SERVER set to 'smtp.example.com', MAIL_PORT set to 587, MAIL_USE_TLS set to True, MAIL_USERNAME set to '[e-mail]', and MAIL_PASSWORD set to 'password123'.

Flask

from flask import Flask
from flask_mail import Mail

app = Flask(__name__)

# Configure email server settings
app.config['MAIL_SERVER'] = 'smtp.example.com'
app.config['MAIL_PORT'] = 587
app.config['MAIL_USE_TLS'] = True
app.config['MAIL_USERNAME'] = '[e-mail]'
app.config['MAIL_PASSWORD'] = 'password123'

mail = Mail(app)

Hint

Set each config key on app.config exactly as shown.

3

Create a route to send an email

Import Message from flask_mail. Define a route /send-email with a function send_email. Inside it, create a Message object with subject 'Hello', sender '[e-mail]', recipients list with '[e-mail]', and body 'This is a test email.'. Then send the message using mail.send(msg).

Flask

from flask import Flask
from flask_mail import Mail
from flask_mail import Message

app = Flask(__name__)
app.config['MAIL_SERVER'] = 'smtp.example.com'
app.config['MAIL_PORT'] = 587
app.config['MAIL_USE_TLS'] = True
app.config['MAIL_USERNAME'] = '[e-mail]'
app.config['MAIL_PASSWORD'] = 'password123'
mail = Mail(app)

@app.route('/send-email')
def send_email():
    # Create Message object
    msg = Message(subject='Hello', sender='[e-mail]', recipients=['[e-mail]'], body='This is a test email.')
    # Send email
    mail.send(msg)
    return 'Email sent!'

Hint

Use @app.route('/send-email') to define the route. Create the Message with the exact subject, sender, recipients, and body. Then call mail.send(msg).

4

Run the Flask app

Add the standard Flask app run block at the bottom: if __name__ == '__main__': and inside it call app.run(debug=True).

Flask

from flask import Flask
from flask_mail import Mail
from flask_mail import Message

app = Flask(__name__)
app.config['MAIL_SERVER'] = 'smtp.example.com'
app.config['MAIL_PORT'] = 587
app.config['MAIL_USE_TLS'] = True
app.config['MAIL_USERNAME'] = '[e-mail]'
app.config['MAIL_PASSWORD'] = 'password123'
mail = Mail(app)

@app.route('/send-email')
def send_email():
    msg = Message(subject='Hello', sender='[e-mail]', recipients=['[e-mail]'], body='This is a test email.')
    mail.send(msg)
    return 'Email sent!'

if __name__ == '__main__':
    # Run the app
    app.run(debug=True)

Hint

Add the standard Flask run block at the end to start the app in debug mode.

Practice

1. What is the main purpose of the Message object in Flask-Mail when sending emails?

easy

A. To configure the mail server settings

B. To hold the email's subject, sender, recipients, and body content

C. To start the Flask application

D. To receive incoming emails

Solution

1. Step 1: Understand the role of Message object

   The Message object is designed to store the email details like subject, sender, recipients, and body.

2. Step 2: Differentiate from other components

   Mail server settings are configured separately, and Flask app startup is unrelated to Message. Receiving emails is not handled by Message.

3. Final Answer:

   To hold the email's subject, sender, recipients, and body content -> Option B

4. Quick Check:

   Message object = email content holder [OK]

Hint: Message object stores email details like subject and body [OK]

Common Mistakes:

• Confusing Message with mail server configuration
• Thinking Message starts the Flask app
• Assuming Message receives emails

2. Which of the following is the correct way to send an email using Flask-Mail after creating a Message object named msg?

easy

A. mail.send(msg)

B. mail.send_message(msg)

C. send.mail(msg)

D. msg.send()

Solution

1. Step 1: Recall Flask-Mail send syntax

   The correct method to send an email is mail.send(msg), where mail is the Mail instance and msg is the Message object.

2. Step 2: Identify incorrect method names

   Options like mail.send_message, send.mail, and msg.send() are not valid Flask-Mail methods.

3. Final Answer:

   mail.send(msg) -> Option A

4. Quick Check:

   Send email = mail.send(msg) [OK]

Hint: Use mail.send() with Message object to send email [OK]

Common Mistakes:

• Using incorrect method names like send_message
• Calling send on the Message object
• Reversing mail and send order

3. Given the following Flask-Mail code snippet, what will be the output or result?

from flask_mail import Message
msg = Message(subject='Hello', sender='[e-mail]', recipients=['[e-mail]'], body='Hi there!')
mail.send(msg)

medium

A. An email with subject 'Hello' is sent from [e-mail] to [e-mail] with body 'Hi there!'

B. SyntaxError because Message requires a different parameter order

C. No email sent because body is missing

D. NameError because mail is not defined

Solution

1. Step 1: Check code completeness

   The snippet uses mail.send(msg) but does not show the mail object being created or initialized.

2. Step 2: Understand Flask-Mail usage

   Without initializing mail with Flask app and configuration, calling mail.send() will cause a NameError because mail is undefined.

3. Final Answer:

   NameError because mail is not defined -> Option D

4. Quick Check:

   Undefined mail object = NameError [OK]

Hint: Ensure mail is initialized before calling mail.send() [OK]

Common Mistakes:

• Assuming mail is auto-created
• Thinking parameter order causes syntax error
• Ignoring missing body error

4. Identify the error in this Flask-Mail email sending code:

msg = Message('Greetings', sender='[e-mail]', recipients='[e-mail]', body='Welcome!')
mail.send(msg)

medium

A. The recipients parameter should be a list, not a string

B. The sender email is missing '@' symbol

C. The Message subject must be passed as a keyword argument

D. mail.send() requires two arguments

Solution

1. Step 1: Check recipients parameter type

   The recipients argument must be a list of email addresses, but here it is a string.

2. Step 2: Validate other parameters

   The sender email is valid, subject can be positional, and mail.send() takes one argument (the Message object).

3. Final Answer:

   The recipients parameter should be a list, not a string -> Option A

4. Quick Check:

   Recipients must be list = The recipients parameter should be a list, not a string [OK]

Hint: Recipients must always be a list, even for one email [OK]

Common Mistakes:

• Passing recipients as a string
• Misplacing subject argument
• Expecting mail.send() to take multiple arguments

5. You want to send an email with Flask-Mail only if the recipient list is not empty and the body text is not empty. Which code snippet correctly implements this check before sending?

hard

A. msg = Message(subject='Hi', sender='[e-mail]', recipients=recipients, body=body)
mail.send(msg)

B. if recipients or body:
msg = Message(subject='Hi', sender='[e-mail]', recipients=recipients, body=body)
mail.send(msg)

C. if recipients and body:
msg = Message(subject='Hi', sender='[e-mail]', recipients=recipients, body=body)
mail.send(msg)

D. if not recipients and not body:
msg = Message(subject='Hi', sender='[e-mail]', recipients=recipients, body=body)
mail.send(msg)

Solution

1. Step 1: Understand the condition logic

   We want to send email only if both recipients and body are not empty, so use if recipients and body:.

2. Step 2: Analyze each option

   if recipients and body: msg = Message(subject='Hi', sender='[e-mail]', recipients=recipients, body=body) mail.send(msg) uses correct and condition. if recipients or body: msg = Message(subject='Hi', sender='[e-mail]', recipients=recipients, body=body) mail.send(msg) uses or which sends email if either is present. if not recipients and not body: msg = Message(subject='Hi', sender='[e-mail]', recipients=recipients, body=body) mail.send(msg) sends email if both are empty (wrong). msg = Message(subject='Hi', sender='[e-mail]', recipients=recipients, body=body) mail.send(msg) sends email unconditionally.

3. Final Answer:

   if recipients and body: msg = Message(subject='Hi', sender='[e-mail]', recipients=recipients, body=body) mail.send(msg) -> Option C

4. Quick Check:

   Send only if both present = if recipients and body: msg = Message(subject='Hi', sender='[e-mail]', recipients=recipients, body=body) mail.send(msg) [OK]

Hint: Use 'and' to check both recipients and body before sending [OK]

Common Mistakes:

• Using 'or' instead of 'and' for condition
• Sending email without any checks
• Checking for empty strings incorrectly