The mailing list is called "hhs89" and is provided as a free service of Yahoo! Groups. Their revenue comes from the small ads at the end of each e-mail sent and the ads on their web site.
If you've never been on a mailing list before, it's quite simple. Any e-mail sent to firstname.lastname@example.org is broadcast to everyone who has subscribed. If you want to change over to a private conversation via e-mail, simply change the "To:" line to the indvidual(s) you wish to converse with. By default, all replies go to everyone on the list.
To subscribe, just use the form below. If you're not already a Yahoo! member, you'll be sent a confirmation message you must respond to. This prevents other people from signing up your e-mail address without your permission.
If you're concerned about privacy, you can simply send a blank e-mail to email@example.com. This method lets you receive and send list e-mails, but does not let you browse the archive or otherwise log on to Yahoo! Groups (unless you've already used that address to sign up for a Yahoo! service). On the up side, you will not be providing Yahoo! with any information beyond your e-mail address. The address for unsubscribing to the list is included at the end of every e-mail sent.