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

We are also facing this problem and we have been troubleshooting this with Microsoft for six weeks. We are now at L3 support and the issue is still not resolved. I understand the AOL Mail and Yahoo Mail have been acquired by Apollo Global Management. I wonder if this issue is an investment issue, at the expense of customer functionality, to reduce the cost of maintaining a mail server. Did anyone get this issue is resolved.

Here our details

Running Windows 11

Outlook 365 (also tried Outlook for Windows same issue)

This only happens after we created a new account profile. It was working for over 20 years.

On an another account that has been around for a while, there is no issue. It looks like this only impacting new users or users with a new profile in Outlook

We also tried the same user account on Windows 10 and it was still limited to 10000

When we configured Thunderbird, we had the same problem and we were limited to 10000 emails as well

So I agree with the last poster in that this is a host issue.

I also saw this article - https://www.reddit.com/r/Thunderbird/comments/v4ydu0/10000\_email\_limit\_via\_imap\_in\_yahoo\_email/

and also this one

https://en-global.help.yahoo.com/kb/SLN28681.html?guccounter=1&guce_referrer=aHR0cHM6Ly93d3cucmVkZGl0LmNvbS8&guce_referrer_sig=AQAAAEELBM4iam3qjjw717BOnVrH2yG2Ipq5i5PlylJrh4CVHCDTZtc3WSp-lIvU6rVN4w-jHFsTqoaoWavo3RioGBMAFGuRLBoauImSru87lK5z3jkOWVtPVbtL4FKZYZX57l0wqU6njRC4z8V5af8Wy4lnK_dUt1eAuwTQviQ-noCD

I did some testing via imap to understand difference between imap.mail.yahoo.com and export.imap.mail.yahoo.com and discovered the following:

If I use export.imap.mail.yahoo.com instead of the normal imap.mail.yahoo.com to retrieve all emails from Yahoo mail servers, it seems to be working as Outlook 365 has started getting more items from the Inbox now.

The count is increasing from 10000 now.

I switched from TBird to Outlook 365 in early February (around Feb 3). The "cycling" of going down to 1000 messages in the Inbox and Sent folders then "re-retrieving" the emails back to 27K (Inbox) and 8K (Sent) caused my Xfinity data usage to increase from less than 300GB/month to 1.6TB for February. I'm at 700GB for March. Fortunately, Xfinity will "forgive" the first time you exceed the 1.2TB/month limit, so I didn't get charged extra for February. To keep from getting charged going forward, I switched to Xfinity's unlimited plan, which costs me an additional $25/month. So now, this issue is costing me real money.

After using my AOL Mail email address since 1990, I think I'm going to take this as a sign that I need to change email addresses and move away from AOL Mail over the next twelve months.

I did some testing via imap to understand difference between imap.mail.yahoo.com and export.imap.mail.yahoo.com and discovered the following:

using imap.mail.yahoo.com

| > openssl s\_client -connect imap.mail.yahoo.com:993 -crlf -quiet
depth=2 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert High Assurance EV Root CA
verify return:1
depth=1 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert SHA2 High Assurance Server CA
verify return:1
depth=0 C = US, ST = California, L = Sunnyvale, O = Oath Holdings Inc., CN = \*.imap.mail.yahoo.com
verify return:1
\* OK Welcome! IMAP Server up and ready to accept your request
tag login {my yahoo email} {my yahoo app password}
tag OK [CAPABILITY IMAP4rev1 ID MOVE NAMESPACE XYMHIGHESTMODSEQ UIDPLUS LITERAL+ CHILDREN UNSELECT X-MSG-EXT OBJECTID IDLE ENABLE UIDONLY X-ALL-MAIL X-UIDONLY LIST-EXTENDED LIST-STATUS SPECIAL-USE MESSAGELIMIT=1000 PARTIAL APPENDLIMIT=41697280] LOGIN completed
tag capability
\* CAPABILITY IMAP4rev1 ID MOVE NAMESPACE XYMHIGHESTMODSEQ UIDPLUS LITERAL+ CHILDREN UNSELECT X-MSG-EXT OBJECTID IDLE ENABLE UIDONLY X-ALL-MAIL X-UIDONLY LIST-EXTENDED LIST-STATUS SPECIAL-USE MESSAGELIMIT=1000 PARTIAL APPENDLIMIT=41697280
tag OK CAPABILITY completed
tag STATUS INBOX (MESSAGES)
\* STATUS "Inbox" (MESSAGES 39499)
tag OK STATUS completed
tag select inbox
\* 10000 EXISTS
\* 0 RECENT
\* OK [UIDVALIDITY 1301025799] UIDs valid
\* OK [UIDNEXT 610530] Predicted next UID
\* FLAGS (\Answered \Deleted \Draft \Flagged \Seen $Forwarded $Junk $NotJunk)
\* OK [PERMANENTFLAGS (\Answered \Deleted \Draft \Flagged \Seen $Forwarded $Junk $NotJunk)] Permanent flags
\* OK [HIGHESTMODSEQ 170930]
\* OK [MAILBOXID (1)] Ok
tag OK [READ-WRITE] SELECT completed; now in selected state
tag enable uidonly
\* ENABLED UIDONLY
tag OK ENABLE completed
tag select inbox
\* 39499 EXISTS
\* 0 RECENT
\* OK [UIDVALIDITY 1301025799] UIDs valid
\* OK [UIDNEXT 610530] Predicted next UID
\* FLAGS (\Answered \Deleted \Draft \Flagged \Seen $Forwarded $Junk $NotJunk)
\* OK [PERMANENTFLAGS (\Answered \Deleted \Draft \Flagged \Seen $Forwarded $Junk $NotJunk)] Permanent flags
\* OK [HIGHESTMODSEQ 170930]
\* OK [MAILBOXID (1)] Ok
tag OK [READ-WRITE] SELECT completed; now in selected state

using export.imap.mail.yahoo.com

| > openssl s\_client -connect export.imap.mail.yahoo.com:993 -crlf -quiet
depth=2 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert High Assurance EV Root CA
verify return:1
depth=1 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert SHA2 High Assurance Server CA
verify return:1
depth=0 C = US, ST = California, L = Sunnyvale, O = Oath Holdings Inc., CN = \*.imap.mail.yahoo.com
verify return:1
\* OK Welcome! IMAP Server up and ready to accept your request
tag login {my yahoo email} {my yahoo app password}
tag OK [CAPABILITY IMAP4rev1 ID MOVE NAMESPACE XYMHIGHESTMODSEQ UIDPLUS LITERAL+ CHILDREN UNSELECT X-MSG-EXT OBJECTID IDLE ENABLE UIDONLY X-ALL-MAIL X-UIDONLY LIST-EXTENDED LIST-STATUS SPECIAL-USE MESSAGELIMIT=1000 PARTIAL APPENDLIMIT=41697280] LOGIN completed
tag capability
\* CAPABILITY IMAP4rev1 ID MOVE NAMESPACE XYMHIGHESTMODSEQ UIDPLUS LITERAL+ CHILDREN UNSELECT X-MSG-EXT OBJECTID IDLE ENABLE UIDONLY X-ALL-MAIL X-UIDONLY LIST-EXTENDED LIST-STATUS SPECIAL-USE MESSAGELIMIT=1000 PARTIAL APPENDLIMIT=41697280
tag OK CAPABILITY completed
tag STATUS INBOX (MESSAGES)
\* STATUS "Inbox" (MESSAGES 39499)
tag OK STATUS completed
tag select inbox
\* 39499 EXISTS
\* 0 RECENT
\* OK [UIDVALIDITY 1301025799] UIDs valid
\* OK [UIDNEXT 610530] Predicted next UID
\* FLAGS (\Answered \Deleted \Draft \Flagged \Seen $Forwarded $Junk $NotJunk)
\* OK [PERMANENTFLAGS (\Answered \Deleted \Draft \Flagged \Seen $Forwarded $Junk $NotJunk)] Permanent flags
\* OK [HIGHESTMODSEQ 170930]
\* OK [MAILBOXID (1)] Ok
tag OK [READ-WRITE] SELECT completed; now in selected state
tag enable uidonly
\* ENABLED UIDONLY
tag OK ENABLE completed
tag select inbox
\* 39499 EXISTS
\* 0 RECENT
\* OK [UIDVALIDITY 1301025799] UIDs valid
\* OK [UIDNEXT 610530] Predicted next UID
\* FLAGS (\Answered \Deleted \Draft \Flagged \Seen $Forwarded $Junk $NotJunk)
\* OK [PERMANENTFLAGS (\Answered \Deleted \Draft \Flagged \Seen $Forwarded $Junk $NotJunk)] Permanent flags
\* OK [HIGHESTMODSEQ 170930]
\* OK [MAILBOXID (1)] Ok
tag OK [READ-WRITE] SELECT completed; now in selected state

The only difference in the two imap outputs above is the number of emails in "exists" upon selecting inbox.

With export.imap.mail.yahoo.com I get all 39499 messages, with imap.mail.yahoo.com I get 10000 messages.

However, if you set the UIDONLY flag, even on imap.mail.yahoo.com, selecting inbox will show all 39k messages. So it seems to be having an effect.

As mentioned elsewhere, the UIDONLY flag seems to be detailed in a draft IMAP extension which was recently updated (March 3 2023: https://datatracker.ietf.org/doc/draft-ietf-extra-imap-uidonly/ ). I don't know how that process works.

My guess is none of the 3rd party tools implement UIDONLY as yet.

This seems pretty clear evidence to me at least that this setting comes from Yahoo - esp since the default tools that connect to yahoo will just use imap.mail.yahoo.com.

I found some documentation in Yahoo's developer documentation which hints at this as well https://senders.yahooinc.com/developer/documentation/#imap-modes-limitedHowever, that Yahoo documentation also talks about MESSAGELIMIT, which in the IMAP results above is "1000" not "10000", so I don't understand how MESSAGELIMIT plays into things here.https://senders.yahooinc.com/developer/documentation/#imap-modes-limitedAsAs to experienced behavior, I haven't tried using the export URL locally, as I've seen reports here about other issues that crop up. With regular imap on OSX mail, I am limited to 10k per folder.

Hopefully some imap gurus can look at this and dig further to discern other differences between the two servers, and maybe understand what is causing 'recycling' (I don't really understand that what means).

You beat me to it. It is a yahoo/AOL issue, starting with the fact that they took it upon themselves to cap the number of emails at 10,000 with no announcement, leaving people looking everywhere else but to them for the cause (until someone looked at the underlying dialog and found that they supplied the count of the number of emails.

The emails are there, using mail.aol.com (or the yahoo equivalent), or the app. I stopped using the AOL app years ago because their searching capabilities were pitiful. Been using various outlook versions since then, and then when this hit, I thought it was on my end until eventually I googled and found this forum. Found the workaround (add the prefix "export." to the imap server), and it got the full emails. EXCEPT it keeps cycling and presumably telling outlook that there are no emails, or otherwise calling for a sync, goes does to 1000 or 2000 per folder (I've seen both at different times).

We were advised that capping folders at 10,000 would stop it so I moved years of data to year specific folders. THOSE folders go down to 2000 (and I can see 2000 in several, eventually filling up). On my older PC especially, the indexing restarts (where it was zero, it was over 100K and slowly counts down). All that syncing and indexing causes the PC to get hot. This is ridiculous.

And to my knowledge they have never come out with a statement of what they did, presumably intentionally, the only usable word they gave is to use their web page or app. If either had been good I would have never gone to outlook.