I need a minimal SMTP daemon written in Python that I can spin up on an Ubuntu box and use solely for functional testing. The server must accept any “MAIL FROM” and “RCPT TO” values so I can spoof sender domains during QA, but it does not have to relay messages to the wider internet. Storing the raw messages locally (file system or SQLite) or printing them to stdout is fine; the key requirement is that the SMTP handshake completes successfully for arbitrary domains. Please keep the footprint light—using the standard library (smtpd / asyncio) or a small dependency such as aiosmtpd is ideal—and provide a clean way to start, stop, and persist the service on Ubuntu (systemd unit is preferred). Deliverables • Python source code for the SMTP server • systemd service file and quick-start README (install, start, stop, log viewing) • Simple configuration knobs: listening port, maximum message size, optional AUTH toggle • A short test script or cURL example that demonstrates sending a message from an arbitrary address and shows where the message is stored Acceptance criteria: After deployment on my Ubuntu VM, I should be able to run a single command to bring the service up, issue an SMTP session from any domain, and see the captured email content immediately. No external MX records, DNS changes, or full mail stack should be required. This is for internal testing purposes only, and I don't need to worry about actual email delivery, spam checks, or any domain authentication like SPF/DKIM/DMARC.