HTML email templates in Flask

Introduction

HTML email templates let you send pretty, styled emails instead of plain text. They make your emails look nice and easy to read.

When sending welcome emails to new users with your brand colors and logo.

When sending order confirmations that show product details clearly.

When sending newsletters with images and links.

When you want your emails to look professional and trustworthy.

When you want to include buttons or styled text in emails.

Syntax

Flask

from flask import Flask, render_template
from flask_mail import Mail, Message

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

mail = Mail(app)

@app.route('/send-email')
def send_email():
    msg = Message('Hello from Flask', sender='[e-mail]', recipients=['[e-mail]'])
    msg.html = render_template('email_template.html', name='Friend')
    mail.send(msg)
    return 'Email sent!'

# email_template.html is a separate HTML file with your email design.

Use render_template to load your HTML email file and fill in dynamic parts.

Set msg.html to the rendered HTML string to send styled emails.

Examples

This loads the HTML template and replaces {{ name }} with 'Alice'.

Flask

msg.html = render_template('email_template.html', name='Alice')

Example of a simple HTML email template using Jinja2 placeholders.

Flask

<html>
  <body>
    <h1>Hello {{ name }}!</h1>
    <p>Welcome to our site.</p>
  </body>
</html>

Sample Program

This Flask app sends a styled HTML email using a simple template string. It replaces {{ name }} with 'Friend'.

Flask

from flask import Flask, render_template_string
from flask_mail import Mail, Message

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

mail = Mail(app)

email_html = '''
<html lang="en">
  <body style="font-family: Arial, sans-serif;">
    <h2 style="color: #2a9d8f;">Hello {{ name }}!</h2>
    <p>Thanks for joining our community.</p>
    <p>We hope you enjoy your stay.</p>
  </body>
</html>
'''

@app.route('/send-email')
def send_email():
    msg = Message('Welcome!', sender='[e-mail]', recipients=['[e-mail]'])
    msg.html = render_template_string(email_html, name='Friend')
    mail.send(msg)
    return 'Email sent!'

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

Important Notes

Always test your HTML email in different email clients to check how it looks.

Keep your HTML simple and inline styles for best compatibility.

Use Flask-Mail to handle sending emails easily in Flask apps.

Summary

HTML email templates make emails look nice and professional.

Use Flask's render_template or render_template_string to create email content.

Send emails with Flask-Mail by setting the html property of the message.

Practice

1. What is the main purpose of using HTML email templates in Flask applications?

easy

A. To create visually appealing and structured email content

B. To speed up the sending of emails

C. To store email addresses securely

D. To encrypt email messages automatically

Solution

1. Step 1: Understand what HTML email templates do

   HTML email templates help format emails with colors, images, and layout to look professional.

2. Step 2: Identify the purpose in Flask context

   Flask uses templates to generate this HTML content dynamically for emails.

3. Final Answer:

   To create visually appealing and structured email content -> Option A

4. Quick Check:

   HTML email templates = visually appealing emails [OK]

Hint: HTML templates make emails look nice and professional [OK]

Common Mistakes:

• Confusing template purpose with email sending speed
• Thinking templates store email addresses
• Assuming templates encrypt emails

2. Which Flask function is commonly used to render an HTML email template from a file?

easy

A. render_template_string()

B. make_response()

C. send_email()

D. render_template()

Solution

1. Step 1: Recall Flask template rendering functions

   Flask provides render_template() to render templates from files and render_template_string() for strings.

2. Step 2: Identify the function for file templates

   For HTML email templates stored as files, render_template() is used.

3. Final Answer:

   render_template() -> Option D

4. Quick Check:

   File template rendering = render_template() [OK]

Hint: Use render_template() for file-based HTML templates [OK]

Common Mistakes:

• Using render_template_string() for file templates
• Confusing send_email() as a Flask function
• Using make_response() for rendering templates

3. Given this Flask code snippet for sending an email, what will be the content type of the email sent?

from flask_mail import Message
msg = Message(subject='Hello', recipients=['[e-mail]'])
msg.html = render_template('email.html', name='Alice')

medium

A. HTML formatted email

B. JSON formatted email

C. Multipart email with attachments

D. Plain text email

Solution

1. Step 1: Check how email content is set

   The code sets msg.html using render_template(), which produces HTML content.

2. Step 2: Understand Flask-Mail behavior

   Setting msg.html sends the email as HTML formatted content.

3. Final Answer:

   HTML formatted email -> Option A

4. Quick Check:

   msg.html set = HTML email [OK]

Hint: Setting msg.html sends HTML email content [OK]

Common Mistakes:

• Assuming plain text because no msg.body set
• Thinking attachments are included automatically
• Confusing JSON format with email content

4. Identify the error in this Flask email template rendering code:

msg = Message('Hi', recipients=['[e-mail]'])
msg.html = render_template('email_template.html')
send_email(msg)

medium

A. render_template() requires variables passed

B. msg.html should be msg.body

C. send_email() is not a Flask-Mail function

D. Message requires sender argument

Solution

1. Step 1: Check Flask-Mail sending function

   Flask-Mail uses mail.send(msg) to send emails, not send_email().

2. Step 2: Verify other parts

   Setting msg.html is correct for HTML content, and sender is optional if configured globally.

3. Final Answer:

   send_email() is not a Flask-Mail function -> Option C

4. Quick Check:

   Flask-Mail send = mail.send() [OK]

Hint: Use mail.send() to send emails, not send_email() [OK]

Common Mistakes:

• Using send_email() instead of mail.send()
• Confusing msg.html with msg.body
• Thinking sender is always required in Message

5. You want to send a personalized HTML email in Flask using a template that includes the user's name and a list of their favorite items. Which approach correctly combines rendering and sending the email?

hard

A. Use render_template_string() without variables, set msg.html, then mail.send(msg)

B. Render template with variables, set msg.html, then use mail.send(msg)

C. Set msg.body with template filename, then call mail.send(msg)

D. Set msg.html to plain text, then call mail.send(msg)

Solution

1. Step 1: Render template with variables

   Use render_template() passing user's name and list to generate HTML content.

2. Step 2: Assign rendered HTML to msg.html and send

   Set msg.html to the rendered content and send with mail.send(msg).

3. Final Answer:

   Render template with variables, set msg.html, then use mail.send(msg) -> Option B

4. Quick Check:

   Render with vars + msg.html + mail.send() = correct [OK]

Hint: Render with variables, assign to msg.html, send with mail.send() [OK]

Common Mistakes:

• Setting msg.body to template filename instead of content
• Not passing variables to render_template()
• Sending plain text in msg.html