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

Seems that yes, just changing the server works.  

Below from Apple forum: - no need for the other software:

https://discussions.apple.com/thread/253810183?page=3 

Search through Yahoo's documentation I found a workaround that allows downloading of all the emails.

It's just a matter of changing the IMAP settings for 3rd party mail apps.

However I had to delete the predefined "Yahoo" account and setup "other mail account".

I entered my account, one-time generated password, had to wait 10-20 seconds to get a time-out

and then was able to enter the IMAP and SMTP settings.

The main change is for the incoming mails:

export.imap.mail.yahoo.com

https://help.yahoo.com/kb/new-mail-for-desktop/download-email-yahoo-mail-third-party-sln28681.html

This solved my issue - and maybe it might help others in the community.

Here's the letter I wrote with intention to send it to the Yahoo corporate office in Sunnyvale addressing specifically the CEO and CTO. I will appreciate any suggestions or corrections to make it better and asking all of you to add your names to the letter

Dear Sirs

I am addressing this directly to the CEO and the CTO of Yahoo Inc since no one in Yahoo Customer Care offered any other escalation path to address an issue that is negatively impacting great many Yahoo Mail customers.

As has been noticed by many Yahoo Mail customers there was an implementation rolling across the US IMAP Servers for Yahoo and AOL Mail. It has been impacting customers at different geographic locations between February and June likely based on the IMAP Servers rollout schedule.

The change impacted all Desktop client software that is used by Yahoo Mail customers who prefer to utilize Desktop email applications rather than Webmail. That includes all versions of Microsoft Outlook (from 2010 to the latest 365) both on Windows and on MacOS platforms, Mac Mail on MacOS, Thunderbird on Windows and possibly others that I am not aware of. I have seen complaints from many dozens to hundreds customers. I do not have the means to accurately estimate the number of people that have been affected, but my guess, it is probably in the hundreds and thousands already, and might reach tenss of thousand if nothing is done to fix the problem.

The direct effects of the IMAP servers software change are as follows

1. When desktop client app starts up and establishes connection to Yahoo or AOL Mail, the IMAP Servers that control that connection limit download of messages to Desktop client to 10000 per folder. Many of the customers prefer keeping longer history in their Desktop Inbox and limiting the number of messages greatly reduces the search ability within their own emails.
   I used to be able to search within 10yrs of may emails, now I am limited to one year or so.
2. One of the responses Yahoo and AOL support gives to people having this problem is to move emails to folders rather than keeping them in the Inbox. We could discuss merits of that advise separately, but it is nearly impossible to follow, because the same IMAP server change limits the number of messages that can be moved as a group from Inbox to a folder to under 20. Imagine trying to move 10000 messages and more to different folders in batches of 20 msgs at a time!!?

However, the most frustrating (bordering on outrageous) part of this is how Yahoo and AOL support reacted to customer questions or complaints. They vehemently deny there was any change made to establish the message limit which is clearly not true. Some of the affected customers were able to issue Open SSL query to IMAP servers that returns only 10000 messages to the Inbox whereas it is expected to return all messages without any limit. Furthermore, freely accessible Yahoo developers webpage documents that the standard IMAP API call that has been used for many years to access the email, now returns only 10000 messages, and a NEW API UIDONLY call needs to be used to download all messages without limit. Yahoo and AOL support, while denying anything changed on their IMAP server side, direct customers to contact vendors of the Desktop client software, such as Microsoft and Apple. Clearly that implies that the vendors would to implement changes based on the NEW IMAP API to be able to download all messages without limit. Needless to say, the vendors tell us that their software does not impose any message limits and downloads what is given to them by IMAP Servers. Yahoo R&D clearly neglected to coordinate their IMAP Servers change with the corresponding required changes on the Desktop client side thus negatively impacting all of the Desktop mail client customers. That is a clear violation of the very basic rules of client server development basic principles and good practices, as well as complete neglect for customer experience. Now Yahoo/AOL is trying to force their customers to put pressure on the Desktop client vendors to backfill their own failure to properly coordinate the changes. Additionally, even if and when Microsoft and Apple make the changes on the email client side to use the NEW UIDONLY API, the client updates will be only rolled to the current Outlook 365 and other latest email client software. That leaves out great multitude of customers who use older versions of Outlook and other email client software that no longer receive vendor updates.

Clearly this change needs to be reversed or backed out until such time when it can be implemented in a smooth and transparent manner.

We are asking the Yahoo/AOL Corporate management to step in right the wrong done to us by this cavalier and neglectful change to the IMAP servers.

I received an email from my Microsoft Support Agent informing me that he is still working on this issue for me (wow!). So, in response I pointed him to this thread and copied and pasted Mark_302's post specifically. I've asked him:

a) does Outlook support the IMAP UIDONLY extension;

b) if so, how can it be activated;

c) if not, is there a way to have this implemented in a future update to Outlook.

I'll let you know when I hear back.

That answer from AOL does not ring true to me. IMAP Servers is what controls the msg download process, so my 40+ years experience in s/w development tells me the server determines how many messages are downloaded. Likely scenario to me they implemented some logic downloading 10000 and then waiting for the client to say give me next 10000 chunk. But the clients have not been made aware of this dialog and do nothing. Such features would only work if both sides participate. Looks like Yahoo/AOL has implemented this change without coordinating with all the clients to do the matching change. This is a NoNo in s/w development

Yahoo and AOL use the same technical platform. Verizon bought Yahoo in 2017 and started merging it with the remnants of AOL which it has purchased earlier. In 2021 they were both sold to private investment fund Apollo. They carry separate brands but share the technical platform.

I doubt the limit is intentional, that would be too idiotic. I do think it is a bug though. It is a major inconvenience for people like us who built email use around desktop client and I intend to continue trying to get it fixed