kmail : 5.11.1
KDE Frameworks 5.58.0
Qt 5.12.3 (built on 5.12.3)
xcb window system

Since my update to above on Arch two weeks ago, kmail does not fecth mail using POP3, not list the INBOX content using IMAP. Content of other folders are listed using IMAP though. This happens for one particular mail server. Three other mail servers continue to work as usual since that update. No error messages in a terminal.

POP3 and IMAP have been tested successfully with Thunderbird, and on an Android smartphone, on that same failing account's server. Besides, when a new user and his kmail accounts are created, the results are the same.

That mail service provider has been OK for years. They did not advertise any fundamental changes recently. It can be accessed normally with Thunderbird and on Android. So I suspect it has to do with kmail/akonadi. Unfortunately, there are no useful error messages when run in a terminal.

I am ready to provide more information upon your instructions, and hope someone may advise usefully.

Thanks.

Still no better with :

kmail : Version 5.11.2
KDE Frameworks 5.58.0
Qt 5.12.3 (built on 5.12.3)

same issue here
kmail simply doesn't list anything in my iMap inbox, there is no error or message after 'Fetching' mail, I have checked and double-checked all iMap settings

email works great when I use Thunderbird or Evolution (it's my own mail server)

KMail version: 5.13.3 (19.12.3)

EDIT:
What's odd actually is that many (all?) of the subfolders do have mail in them, just the "root" folder that has nothing (including new/test messages)