28. Can a list message be "recalled"?
Typically, no. Message "recall" features in mail clients (notably Microsoft Outlook, but possibly others) tend only to work for messages that remain inside a corporate "walled garden", such as Microsoft Exchange. Attempting to use the "recall" feature for messages sent outside of the walled garden simply results in a message being sent to recipient(s) with a subject indicating that the original sender wishes to recall the message.
List messages sent to moderated lists can, in a fashion, be "recalled" – so long as the message has not yet been approved for posting, the sender can notify the moderators not to approve the message (the approval "cookie" will time out eventually, or a moderator can reject it explicitly via the web moderation interface or with an OK CANCEL cookie_code command). But if the moderators have already approved the message, the same answer applies as above.
It is possible for a list owner to easily remove errant postings from the list archives by viewing the indexes in the web archive interface and using the trash bucket icon appearing at the right of each individual posting to delete them. This works for only one message at a time; there is no "bulk-delete" option available for postings. And of course, the message has already been distributed, so subscribers will already have received their copies.
Finally, it is NOT recommended to edit the list's DIGEST file to remove the posting before digest users receive it. LISTSERV is very sensitive to ad-hoc hand-editing of most of its files, and editing the digest before it is cut will likely result in errors which make it impossible to post new messages to the list. This is similar to the problem addressed in FAQ #18, above, and the same fix would be required if this problem were to occur due to the DIGEST file being edited.