So, I've been having some fun, since my Yahoo ID goes back to 2005, and inactive accounts have been purged. Originally, I signed up for a Yahoo account but I linked my hotmail up to receive messages. So I had the hotmail account, but not the Yahoo ID.

What I had to do was set up a new Yahoo account, link that same ID, and then run this tool to make it all sync up:
https://joshuatj.com/2018/07/18/your-email-address-is-not-linked-to-a-yahoo-id-yahoo-groups/

And it let me back to the old mailing lists I was subbed to 15 years ago.