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: email@example.com and firstname.lastname@example.org
Yale Math Competition: email@example.com
Putnam seminar: mailing list (and Zoom links) here. Contact: firstname.lastname@example.org
Math counts outreach: email@example.com