Yahoo SMTP not accepting emails sent from Apple OS Mail app.

In recent months Yahoo had advised users of Apple OS Mail that an app specific password would be required for a one time login to continue using Apple Mail. The reason provided was the OS Mail app does not have adequate security. My wife and I each have an iMac. (One is using Venture 13.7 and the other Sonoma 14.6.1) I created an app specific password for Apple Mail on both devices prior to the posted deadline. Sending emails worked fine after that until last week. Now emails created on both devices are rejected by the Yahoo smtp server. The iOS Mail app on our iPhones work fine. (Yahoo states the iPhone iOS app is more current and has better security than the older (outdated?) OS Mail app.) Is our problem Mac related or Yahoo related?