This is an old revision of the document!
In our standard Usermin webmail, just deleting a message from a folder will cause the folder to be expunged…even if you delete a message that is already marked as deleted.
https://webmail.sonoracomm.com
In RoundCube webmail (handles folders better), select a folder then click on the little 'gear' icon in the lower left corner and choose 'Compact'.
Preferences → Advanced → General → Advanced Configuration → Enable Global Search and Indexer
Account Settings → (each account) → Junk Settings
Preferences → Security → Junk
Reset Training Data
can fix some problems and is global affecting all accounts.