Apple Mail only displaying 10,000 emails

Has AT&T or Yahoo! changed or provided a configuration on the mail server side for the quanta of emails downloaded? As far as I recall, Apple does not state a capacity limitation for emails, and I know others over the years have mentioned orders of magnitude more emails using Apple Mail that your 10K.

same issue here on Yahoo, tried removing account/ rebuilding mailbox, nothing works. Was with Apple support for a couple of hours this week, they found it very intriguing and will escalate but could not fix it. Also starting today some of my emails are being rejected, saying that the certificate cannot be trusted, not sure if related. From the browser in the Yahoo email, I can see all emails, so no cap at 10,000, and I can send/receive no issues, so problem seems to be on the Apple side

Same issue for me on my 2015 iMac that's running Mojave, and my 2015 Macbook Pro that's running Big Sur. The problem is with my AOL emails. In the AOL browser, all 70k emails are there, but not in Mail. I noticed the problem last week. Not certain if it's related, but it happened around the time I updated my laptop from Catalina to Big Sur last week. As of now, both Mail apps show 9,993 emails. One interesting thing...as emails come in, the number of emails stays at 9,993, but the oldest email remains in place. I don't notice any emails being deleted. When I delete emails manually, the number goes down. Please keep us posted with your case! Thanks!

I had the same problem and found the solution yesterday in this thread and it worked for me.

Mail won't retrieve more than 10,000 emai… - Apple Community

see my reply, I have a case pending with Apple, but so far nothing back