The GNU Mailman software collects only your real name, email address and subscription preferences. Your real name is optional and need not be provided. Your email address is used in sending you messages from the email lists to which you subscribe and for verifying your identity when you subscribe to lists, visit list archives or make certain other changes to your subscription settings. Your real name, email address and subscription preferences are available to the administrators of the lists to which you subscribe. In addition, Your real name and email address are included in rosters available to the list administrators, and, depending on list settings, may also be available to other list members.
Also, many lists maintain public archives which are web accessible and indexed in search engines. Other lists maintain archives which are available only to list subscribers, but may allow anyone to subscribe. Anything you post to a list, including your name and email address and any information in the post or its email signature is potentially available to anyone.