How to Send Email with Flask via SMTP

AhaSend lets Flask send transactional email over SMTP; this guide uses Python’s built-in smtplib and a Flask command to keep sending on the server. Before sending, verify your domain and create an SMTP credential. Use a sandbox credential for these examples so no email is delivered. Keep the username and password in your server’s secret store. Use Python 3.13. Set SMTP_USERNAME, SMTP_PASSWORD and AHASEND_FROM in your shell or secret store. A separate Flask mail extension is not needed.

Install Flask

python3.13 -m venv .venv
source .venv/bin/activate
python -m pip install 'Flask>=3.1,<4'

Save this as quick_send.py:

quick_send.py

import os, smtplib, ssl
from email.message import EmailMessage
from flask import Flask
app = Flask(__name__)
with app.app_context():
    message = EmailMessage()
    message["From"] = os.environ["AHASEND_FROM"]
    message["To"] = "recipient@example.com"
    message["Subject"] = "Flask sandbox test"
    message.set_content("Hello from AhaSend")
    with smtplib.SMTP("send.ahasend.com", 587, timeout=10) as smtp:
        smtp.starttls(context=ssl.create_default_context())
        smtp.login(os.environ["SMTP_USERNAME"], os.environ["SMTP_PASSWORD"])
        if smtp.send_message(message):
            raise RuntimeError("A recipient was rejected")
    print("Accepted by SMTP")

Run python quick_send.py. A failure raises an exception and exits with an error.

Add a Flask Command for Your Worker

Save this as app.py. Set AHASEND_TO=recipient@example.com for testing. The command has no public HTTP endpoint. Flask’s command support runs it with the application context active.

app.py

import os, smtplib, ssl
from email.message import EmailMessage
import click
from flask import Flask
app = Flask(__name__)

@app.cli.command("send-welcome")
def send_welcome():
    try:
        names = ("SMTP_USERNAME", "SMTP_PASSWORD", "AHASEND_FROM", "AHASEND_TO")
        if any(not os.environ.get(name) for name in names):
            raise ValueError("Missing configuration")
        message = EmailMessage()
        message["From"] = os.environ["AHASEND_FROM"]
        message["To"] = os.environ["AHASEND_TO"]
        message["Subject"] = "Your account is ready"
        message.set_content("Welcome to your account.")
        message.add_alternative("<p>Welcome to your account.</p>", subtype="html")
        with smtplib.SMTP("send.ahasend.com", 587, timeout=10) as smtp:
            smtp.starttls(context=ssl.create_default_context())
            smtp.login(os.environ["SMTP_USERNAME"], os.environ["SMTP_PASSWORD"])
            if smtp.send_message(message):
                raise RuntimeError("A recipient was rejected")
        click.echo("Accepted by SMTP")
    except (OSError, smtplib.SMTPException, ValueError, RuntimeError):
        raise click.ClickException("Email failed; check the job and SMTP settings.") from None

Run flask --app app send-welcome. SMTP acceptance is not inbox delivery; use delivery webhooks to track the outcome. When moving this into a queue worker, read the recipient from an authorized job, save the job result, and review uncertain submissions before retrying. SMTP has no API idempotency key.

Before sending: verify your domain and create an SMTP credential.
Connection and message rules: SMTP hosts, ports and limits, special headers, sandbox mode, retention and plan features.
Other ways to send: REST API, AhaSend CLI, Node.js SDK and Go SDK.
Delivery events: webhook setup and local webhook testing.

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How to Send Email with Flask via SMTP

Install Flask

Add a Flask Command for Your Worker

​Install Flask

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Install Flask

Add a Flask Command for Your Worker

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