Yahoo (and I guess AOL) email with Outlook 2021, Thunderbird etc.

 I noticed that with Thunderbird there seemed to be a 10,000 email limit on some of my accounts (I have a very old AOL account and a fairly old Yahoo).

This seemed annoying but no more until I tried adding those accounts to my updated Outlook client (now 2021).

At that point the 10,000 limit became a real pain.

Yes, both accounts could do with a bit of "tidying" but with everyone in the world trying to email me with "intersting offers" the accounts were well in excess of 10,000.

I could see all the emails in Yahoo's webmail but actually a real email account suits me better.

So....

A few searches later:

Confirmation of the problem

Why is an IMAP Inbox Only Displaying 10,000 Items When There are Many - Microsoft Community

and, maybe a fix

Download your email from Yahoo Mail with IMAP | New Mail for Desktop Help - SLN28681

Thanks to

RESOLVED - Yahoo!/AOL IMAP collection emails per folder limits (fookes.com)

The key change is to update the incoming server name:

export.imap.mail.yahoo.com 

(replacing imap.mail.yahoo.com)

for AOL

https://help.aol.com/articles/download-your-email-from-aol-mail-with-imap

similarly

export.imap.aol.com

Hope it helps.

PS

Both needed application specific passwords generated for Outlook 2021.