fake_smtp_server.py

import smtpd
import asyncore

class FakeSMTPServer(smtpd.SMTPServer):
    messages = []

    def __init__(*args, **kwargs):
        print('Fake smtp server running on port 2525')
        smtpd.SMTPServer.__init__(*args, **kwargs)
    
    def process_message(self, peer, mailfrom, rcpttos, data, **kwargs):
        self.messages.append(data)

    
if __name__ == '__main__':
    smtp_server = FakeSMTPServer(('localhost', 2525), None)
    try:
        asyncore.loop()
    except KeyboardInterrupt:
        smtp_server.close()
        print(smtp_server.messages)