I'm not sure if it's the message list which is not refreshed, or if it's the automatic "check mail" which doesn't fully work ("Check mail interval" is set to 5 or 15 minutes for all my accounts), but anyway, the new emails received are not displayed into KMail until I manually click the "Check Mail" button, or I manually go into the Inbox folder corresponding (and still, this works only if I were into another folder).

Reproducible: Always

Steps to Reproduce:
1. Go into Inbox folder of the account B;
2. Send an email from account B to account A;
3. Ensure you get the notification "E-Mail Successfully Sent";
4. Wait a number of minutes higher than the number you configured into the auto check interval (5 minutes in my case, so I wait at least 6 minutes).

Actual Results:  
Nothing happens: no notification of new message, no increase of the unread count between parenthesis.
If I move from the Inbox folder of account B into Inbox folder of account A, then the new email is finally displayed. (By the way, because it is displayed instantly when I enter into the folder, I guess that the email have already been retrieved — it was waiting somewhere, hidden. So the bug is probably only a display/notification bug)

Expected Results:  
Before the end of the delay of the configured "Check Mail interval", I should have got a notification of new email, and the unread count between parenthesis should have been increased.
If I already were in the Inbox folder of the account A, then the new mail should have appear into the message list.

This happens for all of my accounts, not just account "A".

I don't know if it could be related, but the search does not work on my KMail: I press "S", the "Find Messages" popup is opened, but whatever search request I try, I get no results at all, just the "Search complete" message at the bottom-left.

Version 5.2.3

Using:
KDE Frameworks 5.23.0
Qt 5.6.1 (built against 5.6.1)
The xcb windowing system