[Users] Deleting messages previously retained on POP server

[Papa Oz.]

Claws newbie here.  I finally had to give up on Eudora. 

I prefer POP to IMAP.

I have several machines.  Each can read the mail.  All are set to leave
mail on the server.  One is designated to archive all the mail.  On
that machine I want to selectively mark messages to be deleted from the
server, but I want to keep them on the client.  

I suppose I could set up the archiver to always delete from the server,
but there are two reasons I would prefer not to do that.  First, since
the archiver fetches periodically, it would delete messages before the
other machines could look at them.  And second, occasionally a message
needs to be reported to the ISP as spam or objectionable, and for that
I need it on the ISP site.  

I downloaded some old archives of this list and poked around a lot.  I
saw some discussions that were sort of similar but not precisely.
Could anyone please give me a clue as to how to selectively delete
messages from the server that have been fetched but left on the
server?  Many thanks.