Here is a good blog post [1] that explains backscatter and some ways to help prevent it. [1] https://willem.com/blog/2019-09-10_fighting-backscatter-spam-at-se

Here is a good blog post [1] that explains backscatter and some ways to help prevent it. [1] https://willem.com/blog/2019-09-10_fighting-backscatter-spam-at-server-level/ https://willem.com/blog/2019-09-10_fighting-backscatter-spam...