Symptoms
Automatic subscription and un-subscription needs to be disabled.
The automatic subscription/un-subscription process is where a recipient can send a message to the mailing list with the word ‘subscribe’ or ‘unsubscribe’ in the subject line. This can sometimes be implemented by a MailTo link in an HTML page.
Resolution
To prevent someone from auto subscribing/unsubscribing to a mailing list you would need to create a rule in Content Filtering to delete the subscription/unsubscription request before it reaches the Mailing List Manager. (NB. In WorkgroupMail v7 the Content Filtering plug-in would need to be licenced). WorkgroupMail plug-ins are processed in the order listed in the Administrator, so Content Filtering must be listed above the Mailing List Manager. You could create a rule to detect incoming messages that are addressed to the mailing list, and that have not been sent by the moderator, and to delete them. Here is an example rule to do this:-
Disallow mailing list auto subscription/unsubscription
Check messages when they arrive. If message sent to *mailinglist@domain.com* and message not sent from *moderator@domain.com* delete message