Sending Email (Flask-Mail)

Sending email means building a message with a subject, recipients, and a body, then handing it to an SMTP server that delivers it to the inbox.

Learn Sending Email (Flask-Mail) in our free Flask course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick…

Part of the free Flask course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

In this lesson you'll build real email payloads with Python's standard library, add HTML bodies and attachments, send one from a route, and see the Flask-Mail equivalent.

Every email is just structured data: a subject , a from address, one or more recipients , and a body . Flask-Mail's Message object holds exactly these fields. Under the hood it's the same structure as Python's standard-library EmailMessage , which we can build and inspect runnably.

The example below assembles a welcome email and prints its headers and body — this is precisely the payload that would be handed to an SMTP server.

The printout shows the subject, the from/to pair, and the body — the four pieces every message needs before it can be sent.

Real product emails are formatted. You send an HTML version for clients that render it and keep a plain-text version as a fallback. Technically this is a multipart/alternative message holding a text/plain and a text/html part.

The runnable example sets the plain body with set_content and adds the HTML with add_alternative , then prints the resulting multipart structure to prove both parts are present.

The common case is sending mail in response to a user action — a contact form, a password reset, an order confirmation. You read the form data, build the message, and send it. The runnable example does all of that against an in-memory "outbox" so you can see it work end to end, and even shows an attachment.

Complete the message below. Replace each ___ to set the recipient and the body.

Your MAIL_USERNAME / MAIL_PASSWORD are wrong, or the provider needs an app-specific password. For Gmail you must create an app password — your normal login won't work over SMTP.

You called mail.send() outside a request or app context (for example in a background thread). Wrap it in with app.app_context(): so Flask-Mail can read your config.

Build personalized newsletters for a list of subscribers.

Lesson complete — your app can reach the inbox!

You built real email payloads with subject, from, recipients, and body, added HTML with a text fallback and an attachment, sent one from a route, and saw the Flask-Mail API.

🚀 Up next: Logging & Monitoring — see what your app is doing in production.

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