Lot's of e-mails arriving, which I believe are spam backscatter https://en.wikipedia.org/wiki/Backscatter_(email) That article says it is possible to filter those messages, is it doable in ISPConfig? I run ISPConfig 3.1.11 on Debian 9.4. Or is there some other way to reduce those messages? SPF is used, but are those mail servers that send me that backscatter checking the approved senders?
Maybe this may help: http://www.postfix.org/BACKSCATTER_README.html chapter "How do I block backscatter mail to real recipient addresses?" In ISPConfig, you can add header and body checks.
