Here are some mailing lists that you might be interested in joining.
Math DUS news: Click here for more information, and sign up for the DUS mailing list here
YUMS: Link to self-add. Contact: firstname.lastname@example.org and email@example.com
Yale Math Competition: firstname.lastname@example.org
Putnam seminar: mailing list (and Zoom links) here. Contact: email@example.com
Math counts outreach: firstname.lastname@example.org