is it possible to configure Postfix to verify the sender's MX record?
For example: if a mail comes in from
firstname.lastname@example.org it should look up the MX record(s) for
example.com and verify that the sending mail server is listed in the MX records.
Is this possible and does it make sense to block spam mails? Or is there another way to stop spam mails pretending to come from trustworthy domains?