@Girgias Can you edit your DNS records? If possible, I will send you an example of the DNS record description via DM, so please try rewriting the spf record with it.
FYI, mailing lists and spam email are the same in that the email is sent from a server that cannot authenticate your domain.
Therefore, only the domain owner can take action. If countermeasures could be taken on the server side, it would be impossible to identify spam emails.