KMail re-downloads POP3 emails that are supposed to be deleted

Hi,


I am currently struggling with KMail 5.24.5 ignoring my delete-emails-
after-30-days setting and even re-downloading all emails repeatedly. I am 
currently dealing with approx. 1300 unread emails as a result of this issue.

a) How do I stop this behavior?

b) How do I get rid of all unread emails, which I know to be duplicates. I 
tried creating a filter that moves all unread messages to the trash, but 
applying the filter does nothing, even though I can clearly see that it is 
iterating over emails in the filter log.

This is the filter:

[Filter #0]
Applicability=0
AutomaticName=false
ConfigureShortcut=true
ConfigureToolbar=false
Enabled=true
Icon=albumfolder-user-trash
StopProcessingHere=true
ToolbarName=Delete all unread messages
action-args-0=Local Folders/trash
action-name-0=transfer
actions=1
apply-on=
contentsA=Unread
fieldA=<status>
funcA=contains
identifier=pIBl9xxB28oaynAq
name=Delete all unread messages
operator=and
rules=1

[General]
filters=1


Kind regards
MoC

[Filter #0]
Applicability=0
AutomaticName=false
ConfigureShortcut=true
ConfigureToolbar=false
Enabled=true
Icon=albumfolder-user-trash
StopProcessingHere=true
ToolbarName=Delete all unread messages
action-args-0=Local Folders/trash
action-name-0=transfer
actions=1
apply-on=
contentsA=Unread
fieldA=<status>
funcA=contains
identifier=pIBl9xxB28oaynAq
name=Delete all unread messages
operator=and
rules=1

[General]
filters=1