What is “vacuuming”?
A recent trend in “spamming” has been to collect lists of e-mail addresses from various places and sell the lists to commercial entities who spam individuals rather than entire lists, thereby bypassing the spam filter built into LISTSERV. One of the primary sources of these e-mail address lists is LISTSERV subscriber lists. Some have even gone so far on lists where Review=Private as to subscribe to various lists, set their subscription to NOMAIL and then REVIEW the list for the addresses. By using Review=Owner, the list of subscribers is unavailable even to members of the list. The owner of the list can, of course, send out the list when requested, but has the chance to check on the legitimacy of the request. If you do not want to set Review=Owner, you should remind your subscribers that they have the option to CONCEAL their e-mail addresses with the SET listname CONCEAL command.
