Directory Harvest Attacks (DHAs) are a sophisticated technique that spammers use to bypass typical email server checking mechanisms in order to access directories and receive a list of valid email addresses. During a DHA, spammers attempt to deliver messages to multiple addresses, such as johndoe@yourcompany.com, jdoe@yourcompany.com, and john@yourcompany.com. Addresses that are not rejected by the receiving mail server are determined as valid. These addresses are compiled and sold to other spammers worldwide. This is why a brand new email box can be full of unsolicited, junk email just hours after it has been set-up.
