Email address harvesting

The simplest method involves spammers purchasing or trading lists of email addresses from other spammers.
Another common method is the use of special software known as "harvesting bots" or "harvesters", which spider Web pages, postings on Usenet, mailing list archives, internet forums and other online sources to obtain email addresses from public data.
Spammers may also use a form of dictionary attack in order to harvest email addresses, known as a directory harvest attack, where valid email addresses at a specific domain are found by guessing email address using common usernames in email addresses at that domain. For example, trying alan@example.com, alana@example.com, alanb@example.com, etc. and any that are accepted for delivery by the recipient email server, instead of rejected, are added to the list of theoretically valid email addresses for that domain.

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