I have a mail server configured to use DNS real-time blacklists (DNSRBLs), e.g. zen.spamhaus.org, to determine whether delivered email is spam or not.
I would like to evaluate my mail server's configuration since I am still receiving A LOT of spam.
How can I do that? Is it possible to somehow send an email from a blacklisted server for test purposes? Are such blacklisted test servers available at hand?