SUMMARY
Changing a configuration for a POP3 Resource (either via kmail -> settings --> accounts, or akonadiconsole --> Agents --> (select any POP3 resource) --> Configure Natively) is not valued immediately.

STEPS TO REPRODUCE
In akonadiconsole choose a POP3 Resource:
1. Use the "Configure Remotely" to check the id of the associated TargetCollection (i. e. inbox folder)
2. Use the "Configure Natively" dialog of a pop3 resource to change the inbox folder.
3. Again, under "Configure Remotely" the TargetCollection is not updated (Restart Agent is required for this update).
4. Testmails sent to the POP3 Resources are still being put in the outdated (old) target collection.
5. The same holds for configuration changes from kmail (uses the native configuration dialog).

(This also holds for other configuration items.)

OBSERVED RESULT
Configuration updates are not valued when used. The agent (or akonadi as a whole) has to be restarted manually.

EXPECTED RESULT
Configuration updates are valued immediately after being set in the dialog.

SOFTWARE/OS VERSIONS
Linux
(available in About System)
KDE Plasma Version: 5.85.0-r3
KDE Frameworks Version: 5.85.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
Changing an imap resource via the native dialog triggers an automatic agent restart. Maybe that's the way to go for pop3.