A directory harvest attack (DHA) is a technique or method used by spammers to find valid email addresses at a domain. A DHA uses a trial-and-error strategy called a brute force attack or exhaustive key search in an attempt to discover valid or existing email addresses in an SMTP mail server. The brute force approach tries all possible alphanumeric combinations used for a common username, which is the part that comes before the @domain of an email address.

Directory Harvest Attack (DHA)