On October 12, The Yahoo Groups team sent an email to me and, I would guess, every other subscriber of the Arlington Amateur Radio Club's members-only Yahoo group. The important paragraph is:
Beginning December 15, 2020 the Yahoo Groups website will shut down and members will no longer be able to send or receive emails from Yahoo Groups. We’ve compiled a comprehensive FAQ here that includes alternative providers and information on how this will impact your group content.
Arlington Amateur Radio Club President Gary KC5QCN has said he has a plan to migrate members-only emal to a new host, which would also host the w4wvp.org website.
If you have an account on the Yahoo ArlingtonARC site, this is a good time to delete messages that you don't want to save, then download messages that you do want to save to your device, or cloud, then delete _those_ messages on the Yahoo site.