I had not looked into my spamfolder for some time. (Normally I do that once a week.) I saw that quit a few messages of this list ended up there. Mostly because of:
 3.3 RCVD_IN_SBL_CSS        RBL: Received via a relay in Spamhaus SBL-CSS
                            [2600:3c00:0:0:f03c:91ff:fe96:b959 listed in]
                            [zen.spamhaus.org]

Is that something of the list itself, or is it a problem generated by the sender?