Hello! Lately I have problems with SPAM on my ISPconfig servers. More specifically, my clients are getting mail from themselves or some other mail address in their domain. Eg. firstname.lastname@example.org is getting mail from email@example.com (from himself) or from firstname.lastname@example.org (and 'epson' user does not exist). How to prevent that? Is there a way to 'forbid' spoofed email addresses? Note that there is a SPF record on the DNS server for that domain and mail-tester.com gives 9/10 score on that domain.