Dictionary spamming is a spamming technique where spammers attempt to guess E-mail addresses by using a dictionary attack based on adding plausible names as prefixes to known domain names.
The names used are typically generated from a dictionary of common names and surnames, or culled from already-known E-mail addresses: a wide variety of common E-mail address naming conventions will typically be tried. Although most of the generated names will not exist, the effort is generally worth it for the spammers, as a discovered E-mail address may then be used for many subsequent spam runs. The aim is not to discover all possible E-mail addresses: just discovering the "low-hanging fruit" is sufficient to meet the spammers' goals.
In many cases a short test E-mail will first be sent to check for a bounce message. Another common way of verifying E-mail addresses is the use of links to external images in HTML E-mail. By making the links to the images into unique identifiers, it is possible to reconcile hits on the image server with the E-mail address, verifying not only that the E-mail does not bounce, but that it has been viewed in an E-mail client. Finally, clicks on external links in spammed E-mails can be used to verify not only that there is a human being using the E-mail address, but also that they are likely to click spammed links.