On Sat, 16 Mar 2019 at 09:57, Johannes Bauer <dfnsonfsdu...@gmx.de> wrote: > > ...
Do any of your users relay incoming emails via your server into their own mailboxes on Gmail/hotmail? In this case, spam they are *receiving* (not sending) is nevertheless being passed to Gmail/Hotmail by your mail server which might explain why you repeatedly get blacklisted. Tackle this with effective spam blocking on your server and by having your server react when it receives a warning from an onward server about a 'bad' email (e.g. by banning the sender for a period).
