If you are a mail server administrator concerned about being targeted by users of this tool, here are proven countermeasures:
To use the tool effectively (or defend against it), you must understand its internal logic. Here is a step-by-step breakdown of a typical scanning session: Speed Smtp Scanner V2.5 Free Download
Use rate limiting to block IPs that make too many connections or attempts within a short time. For Postfix: If you are a mail server administrator concerned
smtpd_client_connection_rate_limit = 10
smtpd_client_message_rate_limit = 10