subscribein the message's body or subject (but not both).
Within minutes (or sometimes hours), you should receive an e-mail from firstname.lastname@example.org asking for confirmation. Follow the instructions in the e-mail.
You could also follow this link to subscribe to the mailing list.
Similarly, to unsubscribe from the list, send e-mail to email@example.com with the line
unsubscribein the message's body or subject (but not both).