I have disabled non-subscriber post as of May 5 noon GMT. So, let me know if you still receive them.
Also, I have been filtering out about 90% of spam post which was posted to marimba-ebbs even before that.
Having said that, there is nothing that I can do to the spammer putting marimba-ebbs as the from address to spam you. It has nothing to do with this server, and it is not something that I can control.
I would also like you to know that the site is not infiltrated nor used as a bot.
It is just another common spam attack.