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The actual e-mail message generated to the recipient addresses will usually be a short random phrase such as "hello", so as not to trigger a spam filter. Although the attack could also rely on Delivery Status Notifications (DSNs) to be sent to the sender address to notify of delivery failures, directory harvest attacks likely don't use a valid sender e-mail address. Any addresses to which email is accepted are considered valid and are added to the spammer's list (which is commonly sold between spammers). The success of a directory harvest attack relies on the recipient e-mail server rejecting e-mail sent to invalid recipient e-mail addresses during the Simple Mail Transfer Protocol (SMTP) session. This would be considered a standard dictionary attack when guessing usernames for e-mail addresses.

The other, more targeted technique, is to create a list that combines common first name and surnames and initials (as in the example above). For example, one would have to try 36 8 (nearly 3 trillion) e-mail addresses to exhaust all 8-character sequences. This technique would be impractical for usernames longer than 5-7 characters. This would be described as a standard brute force attack. In the first, the spammer creates a list of all possible combinations of letters and numbers up to a maximum length and then appends the domain name. or are two main techniques for generating the addresses that a DHA targets. These attacks are more effective for finding e-mail addresses of companies since they are likely to have a standard format for official e-mail aliases (i.e. The attack is usually carried out by way of a standard dictionary attack, where valid e-mail addresses are found by brute force guessing valid e-mail addresses at a domain using different permutations of common usernames.

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