Another good reason to move to groups.io! Yahoo is also making it harder to use none Yahoo email addresses in their groups.
From: email@example.com [mailto:firstname.lastname@example.org]
Sent: Wednesday, January 31, 2018 12:33 PM
Subject: [IC-7000] Slow Posting by Yahoo
If you notice replies that seem out of order or duplicate something already sugested, my last post took four days to eventually show up in the Group. It was made via the web interface, not e-mail. Other times they show up in minutes. This isn't a new problem, but seems to be getting more frequent the past few months.