I am running exim4 on a vanilla Debian Stable system. The machine has proper DNS A and MX records. I want to use it as a mail server.
SMTP with TLS already works fine for authenticated users.
However I can still telnet from somewhere else to the server using smtp and send mails to my own domain by spoofing the MAIL FROM and picking the right RCPT TO.
How can I configure exim so that only real mail hosts with MX record can use unauthenticated SMTP?