This is the Lists → Mailing List → Subscriptions Tab
The Mailing list Subscriptions tab lets you configure how VPOP3 allows and handles list subscription and unsubscription requests.
The Allow people to subscribe to the list themselves option allows people to email listserver@<your domain> with a message containing 'subscribe <listname>' in the message subject or content to add themselves to the list membership. If this is not checked, then only a VPOP3 administrator or list moderator can add members.
The Inform the list moderators of any new subscriptions or unsubscriptions option tells VPOP3 to send a message to the list moderator(s) (defined on the Other tab) when someone subscribes to or unsubscribes from the list.
The Inform the list moderators of any unsubscriptions option tells VPOP3 to send a message to the list moderator(s) (defined on the Other tab) when someone unsubscribes from the list.
The Verify list subscriptions option sends an email to someone who subscribes to the list, asking them to confirm that they wish to join the list. This is recommended nowadays to prevent people being added to lists without their knowledge.
The This list is confidential option means that the results of the Listserver Lists command will not include this list.
The Use a custom welcome message option means that VPOP3 will send the contents of the Custom Welcome Message box to a new subscriber to the list, instead of a basic built-in message.
The Send a welcome message when moderator adds list member option means that VPOP3 will send the welcome message when a moderator adds a member, as well as when the member subscribes themselves. If this is not checked, the a welcome message is only sent when someone subscribes themselves.
The ListServer for this list option is only available in VPOP3 Enterprise. This indicates which Listserver manages this mailing list. For instance, if your VPOP3 handles multiple domains, you may want different list servers for the different domains. "*" means the generic Listserver@<local domain> address is used, otherwise enter the email address of the list server you wish to create or use.
The Custom Welcome Message box lets you create a custom message which is sent to new list subscribers.
The Use a custom unsubscribe message option means that VPOP3 will send the contents of the Custom Unsubscribe Message box to someone who unsubscribes from the list, instead of a basic built-in message.
The Custom Unsubscribe Message box lets you create a custom message which is sent to people who unsubscribe from the list.