Lately I have a lot of spam coming thru - despite SpamAssassin turned on.

I found the following rule as the root cause:
Many Spam mails received a -5 score from RCVD_IN_DNSWL_HI hence having a low over all spam score.

Thanks to this hint I made a one-line file "repair_RCVD_IN_DNSWL_HI.cf":
score RCVD_IN_DNSWL_HI 0 -0.1 0 -0.1
and added it to MailPlus Server
"SpamAssasin Rules" > Import

Now this rule downgrades spam only by -0.1 so most of it gets caught due to the other rules in place.

Hope this helps…
paradeiser