Rejecting false "mail from" addresses
By default any connection made to ZCS postfix and declares "mail from: local sender" (even if it is not) - the connection/email is accepted for local delivery. This wiki provides steps to block such connections. Once following is configured, postfix will accept "mail from: local sender" only if the connection made from a hosts in "mynetworks" OR the sender is sasl authenticated.
- Modify "smtpd_sender_restrictions". We are adding a check before allowing a normal smtp connection. Allowing hosts in mynetwork, then allowing sasl authenticated too. Then a check for local domain address. If its true - the connection will be rejected.
su - zimbra zmlocalconfig -e postfix_smtpd_sender_restrictions="reject_unknown_sender_domain, permit_mynetworks, permit_sasl_authenticated, check_sender_access hash:/opt/zimbra/postfix/conf/access_table, permit"
- Create the file "/opt/zimbra/postfix/conf/access_table" and add your domain(s) to it.
localdomain.com REJECT anotherlocaldomain.com REJECT
You can also put some friendly/non-friendly message. Something like this.
localdomain.com REJECT You're not me! anotherlocaldomain.com REJECT You're not me!
- Create the hash of "/opt/zimbra/postfix/conf/access_table".
- Restart zmmtactl.
Make following connection from a non-local host which is not defined in mynetworks.
telnet ZCS_server_address 25 mail from: firstname.lastname@example.org rcpt to: email@example.com
You should get following error at the rcpt command.
554 5.7.1 <firstname.lastname@example.org>: Sender address rejected: You're not me!