Clicking on the link [subscribe] (or [unsubscribe]) above should
open your email client. You then simply need to send the email.
If clicking the above link does not work, manually send an email to firstname.lastname@example.org
with the subject subscribe [list name] [your first name] [your last name]
(unsubscribe instead of subscribe to unsubscribe).
[list name] is one of openair5g-user, openair5g-devel, openaircn-user,
openaircn-devel depending on which mailing list you want to subscribe to