A simple Python socketserver.StreamRequestHandler that implements a very basic threaded SMTP server (no TLS/SSL or authentication) that simply reads the email message submitted and discards the data. You might find this useful for performance testing an SMTP client, or gauging network capacity. You should be able to run with Python 3.x and just
python ./smtp_sink.py
The smtp_client.jmx file is a Jmeter workload that can be used to exercise the sink script.