This prober sends mails to a non-existing user in a domain, which will trigger a Delivery Status Notification (DSN). Thus the prober forces the domain's private DNS resolver to query a specified ADNS (to query the MX record of the sender so that the DSN can be sent back).
Use this prober PROPERLY. Do NOT use this prober to flood others' mail servers. Carefully think about INTERNET ETHICS before use.