gistfile1.txt

# mail.example.com should be one of the results of a `dig +short mx example.com`
# Note that your provider might block all port 25.
# If STARTTLS header is missing or mangled, but https://starttls.info/ shows example.com as supporting STARTTLS,
# there might be a downgrade going on.
(echo EHLO foo ; sleep 3) | nc mail.example.com 25