You are experiencing an issue where emails that were moved out of the junk folder are returning back to junk. You have tried to reindex. It is occurring only on Thunderbird but not Webmail
Kerio Connect's rules (both server-side and client-side via the Webmail) only work on new messages that arrive at the user's mailbox. There are no rules that can be set to move messages between different folders after it was already received.
Moreover, as the issue is only reproducible on Thunderbird and not Webmail, it is a client-end problem.
For Thunderbird, clearing the junk filter training cache usually resolves this issue. To clear out the junk filter training cache, please follow these steps:
- In Thunderbird, navigate to ≡ > Preferences > Privacy & Security > Junk
- Press the “Reset Training Data” button