A mailing list is an address that has been configured to broadcast all messages it receives.
Mailing lists in Bitmessage are used the same way mailing lists in a regular E-Mail system is used. members of a list write messages to it and the list server sends a copy of the message to everybody in the subscription list. In Bitmessage clients can send messages to a list without being a member.
Become a member
This is easy, a user needs to add an adress to his Subscriptions.
Create a list
To create a list, an address must be generated first. In the official PyBitmessage client, an address can be promoted to a Mailing list by right click on it and then change the special address behavior to "Behave as a preudo-mailing-list address". A name can be defined, this is used as prefix for broadcasts made by this mailing list, so if a client sends a message with the subject TEST to a list named YAY, it will look like this in response: [YAY] TEST.
A public list that includes mailing lists can be found in the forum.