Yahoo? They limit you to the last 10,000 messages.

Thank you Matt. Is this really a YAHOO imposed limitation or is it a Thunderbird one? Whatever; I suppose I have to workaround by moving stuff I can see from the inbox into other folders. I have observed that when I delete stuff I no longer want, I get to see older emails, so that should work. Thanks again, Zyg

Changing the server by appending 'export' to the name might work:

https://www.reddit.com/r/Thunderbird/comments/vxtae0/aol_and_yahoo_imap_emails_limited_to_10000/

https://www.reddit.com/r/Thunderbird/comments/v4ydu0/10000_email_limit_via_imap_in_yahoo_email/

Yahoo is largely a failed internet company in my opinion. They continue to exist but are largely a spent force outside of the USA. They do mail and really do not document very much at all about that. The user is left to read between the lines of what they do say, and often to filter out the plain destructive advice they offer masquerading a "user support"

Yahoo offer these settings for IMAP. https://help.yahoo.com/kb/imap-server-settings-yahoo-mail-sln4075.html

Then at the bottom of the instructions make some comment about not seeing all of your old mail, and link to this. https://help.yahoo.com/kb/download-email-yahoo-mail-imap-sln28681.html

This later page talks about needing two way syncing and refers you back to the first page.

So to read between the lines. Yahoo offer some form of non standard IMAP which only downloads mail using an apparent IMAP server of the name export.imap.mail.yahoo.com this appears on the face of it to be a download only service, but I honestly do not understand how such a thing could exist and still be called IMAP. They also offer real IMAP server using the name imap.mail.yahoo.com but somehow limit the mail that it will download to local storage.

I can understand their reluctance to fully synchronization huge mail stores as it probably is quite costly. Just uploading and downloading the theoretical 1 terabyte of mail in each account must cost them dearly. Let alone the constant updates and readjustments as folks move their mail from folder to folder. But they are the ones that offered huge free storage for mail of 1 terabyte. Google offered 15Gb and don't appear to have an issue where the infrastructure is not in keeping with the marketing promises. .

As a clueless innocent in this domain I now have a bit of a headache. Thank you guys (for your help that is , the headache is some yahoo's fault). Cheers, Zyg