Strange Mail-Spam issue

Hi,
when i looked up the Mail-Statistics which showed in the email Security extension, i realised, that most of the spam comes from strange mailadresses which don't really exist.

<SRS0=0+PX=WS=grenomdes.store=null@domain.de>

Click to expand...

for example.
How can i find out from where this mail comes and better: stop these mails?