vocal notification for new message received worked fine before frontier moved mail support to yahoo (locked duplicate)

I have set my thunderbird email to vocal announcement for new mail, "You have new mail". This worked fine for years until frontier moved email service to yahoo. Now I get the vocal announcement for new mail infrequently. I suspect that this happens when yahoo "sees" the message first. I contacted yahoo mail support, their response was that this is a thunderbird problem and not yahoo's problem.