I've increased retention in the main bulk of newsgroups to 210 days, if you don't need so much just set your maximal server retention in the days/date field of the search bar, the setting will also persist after restarting the program.
Previous configuration was 150 days / 50 day emergency mode now it is like 210 days and still space to go more and 150 day emergency mode (emergency mode means e.g. if hardware fails I'm still able to reconfigure the service to run at 150 days retention until the problem is fixed).