Python

Before you start

• Python 3.6 or later

1Send a test message

import smtplib
from email.message import EmailMessage

message = EmailMessage()
message['From'] = 'staging@example.com'
message['To'] = 'anyone@example.com'
message['Subject'] = 'Sandbox check'
message.set_content('Hello from Python.')

with smtplib.SMTP('smtp.mailclutch.com', 587) as smtp:
    smtp.starttls()
    smtp.login('mc_0000000000000000', 'pw_0000000000000000')
    smtp.send_message(message)

starttls() before login(): the credentials must not leave the process in the clear, and the server refuses AUTH before the upgrade.

2Or on port 465

with smtplib.SMTP_SSL('smtp.mailclutch.com', 465) as smtp:
    smtp.login('mc_0000000000000000', 'pw_0000000000000000')
    smtp.send_message(message)

Watch it land

Open the sandbox and the message is there — rendered HTML, plain text, raw source, attachments, and the SPF, DKIM and DMARC verdicts. It updates live, so you can leave it open next to your terminal.

Nothing is ever delivered onward, whatever address you send to; claim the inbox with an account and it stays.

What usually goes wrong

• An HTML body

  message.add_alternative('<h1>Hello</h1>', subtype='html') adds the HTML part next to the text one, which is what a real application sends.

• Flask, FastAPI, Celery

  Anything built on smtplib takes the same four values. In Flask-Mail they are MAIL_SERVER, MAIL_PORT, MAIL_USERNAME, MAIL_PASSWORD, plus MAIL_USE_TLS = True.

Other stacks

The same four values in another dialect. Every guide below is filled in with the sandbox pair at the top of this page.