Why is an IMAP Inbox Only Displaying 10,000 Items When There are Many More Emails on the Server?

The point is that AOL Product Report responded with a request to send information to either their Twitter or Facebook social media accounts. I went ahead and sent a tweet to AOL and they responded soon after asking for my email address, and they said they would pass along my comments to their Engineering team. Here is what I sent to AOL's Twitter address (for whatever good it will do):

"Stop limiting 3rd party email applications to the most recent 10,000 messages! This change in your software was implemented without prior notice and is a disservice to users of AOL like myself who have been AOL users for over 30 years. This change in your software makes it impossible to sort and search for emails older than two months, as the online AOL Mail client is insufficient for this purpose. I and many other AOL users take great offense to AOL's unilateral and unannounced change to its software that limits 3rd party email applications to a maximum of 10,000 viewable emails. Your new email format does nothing to mitigate the damage caused to your user base. AOL must reverse this change immediately! This is a serious matter which must be elevated to AOL top management at once. The problem has been confirmed to originate with recent changes to AOL/Yahoo IMAP protocols and not with the 3rd party email applications. Your AOL users insist you take immediate corrective action! See details at https://answers.microsoft.com/en-us/outlook\_com/forum/all/why-is-an-imap-inbox-only-displaying-10000-items/6d15de5f-9047-4b41-9b58-1d8345bbd002"

UPDATE: I changed the Windows registry key data values to something higher than 10000 (decimal) but it didn't have any affect. As a workaround, I thought I would move some of the Inbox mail items (using AOL webmail) to the Archive folder and then let it sync to Outlook so that I could move the emails to an offline PST file. This was a pain in the neck because of AOL's clumsy webmail interface, as I could only move just one or two days' worth of emails at a time. Then I sat back and watched Outlook do its sync thing, and guess what --- the sync stopped once the Archive folder in Outlook reached 10,000 emails.

Maybe he is referring to the below reply as 'evidence' since AOL escalated tech support claimed it was 'working as intended?' https://discussions.apple.com/thread/253810183?page=3 

The mail list discourse thread keyword 'messagelimit' is interesting.

Seems to echo some of our respective concerns:

https://mailarchive.ietf.org/arch/search/?q=messagelimit&f_from=Timo%20Sirainen 

https://mailarchive.ietf.org/arch/search/?q=messagelimit

https://datatracker.ietf.org/doc/html/draft-melnikov-imap-partial-04

It seems affected users are now "IMAP PARTIAL" /Limited Mode? Default

Partial

The Yahoo/Aol IMAP server supports the IMAP PARTIAL allowing clients to walk through a mailbox without using sequence numbers.

Clients should first fetch MESSAGELIMIT capability and keep the message requests below the server announced MESSAGELIMIT.

UID Mode

The clients will be able to fetch and operate on all messages on the mailbox using UIDs. 

This mode is enabled/activated by enabling the “UIDONLY" extension.

All Mail (Experimental)

The Yahoo/Aol IMAP server supports an “All Mail” folder that lists all messages in a user's mailbox. IMAP Clients can use IMAP CONDSTORE & QRESYNC queries to identify new messages, updates and deletes across the entire mailbox.

So after denying it and blaming the mail client, now they say it was a "feature". For them, or for us? Is there a way to opt out of that feature?

I do need to point out that I see no evidence from that post that AOL said that. Looks like the poster is reporting it, and as evidence, the poster has a screen shot (so no proof what it is and where it came from, and even ignoring that, there is no statement to match the post. Looks like AOL support asking for someone to contact them to investigate this problem.

There is no problem with Gmail or Hotmail that i have seen.