Subscribing/Unsubscribing via Email Commands
To subscribe to or unsubscribe from a mailing list, send an email message addressed to MDaemon (or any alias thereof) at the domain hosting the mailing list, and place the Subscribe or Unsubscribe command as the first line of the message body. For example, there is a mailing list called MD-Support being hosted by altn.com. You can subscribe to the list by composing a message addressed to "firstname.lastname@example.org" and placing the value: SUBSCRIBE MD-Support@altn.com as the first line of the message body. The message subject is irrelevant and can be left blank.
For complete details on how to form this and other control messages, see: Remote Server Control Via Email.
Occasionally, users will attempt to subscribe/unsubscribe to lists via email by sending the commands to the list itself rather than to the MDaemon system account. This results in the command being posted to the list rather than the user being subscribed or unsubscribed. To help prevent these sorts of messages from being posted to mailing lists, there is an option located at Setup » Preferences » System, called "Screen incoming mailing list mail for obvious non-list content." This option is enabled by default.
Subscribing/Unsubscribing via Email Addresses
The option, "Honor '<List>-subscribe' and '<List>-unsubscribe' addresses," located at Setup » Preferences » Miscellaneous, makes it possible for users to join or quit mailing lists by sending a message to a special email address rather than requiring them to use the email commands described in Subscribing/Unsubscribing via Email Commands above. To use this method to join or quit a list, a user would simply send a message to the list's address, but with "-subscribe" or "-unsubscribe" appended to the mailbox portion of the address. For example, if the list's name is, "email@example.com," then a user could subscribe to the list by sending a message to, "firstname.lastname@example.org." To unsubscribe from the list, the message would be sent to, "email@example.com." In both cases the content of the subject and message body is irrelevant. Also, when this feature is active MDaemon will insert the following header into all list messages:
Some mail clients can pick up on this and make an UNSUBSCRIBE button available to users automatically.
Subscribing/Unsubscribing via Auto-responders
You can also utilize Auto Responders to automatically add or remove list members. To do this you would create one or more MDaemon accounts whose sole purpose would typically be to automatically add or remove addresses who send messages to those accounts, via the auto responders configured for each account. For example, if you had a mailing list called, "firstname.lastname@example.org," then you could create an MDaemon account with the address: "email@example.com." You would then configure an auto-responder for that account to add to "firstname.lastname@example.org" any addresses sending messages to it. Then, to join that list, all someone would have to do is send an email to "email@example.com". This is a simple solution for users because it doesn't require them to remember any of the special email commands required by the Subscribing/Unsubscribing via Email Commands method outlined above.