RestrictPostfixRecipients

Restrict Postfix Recipients

• This will show how you can modify postfix to restrict who can send to certain addresses in your domain such as distribution lists like all@mydomain.com
• These changes will most likely not persist between upgrades! (UPDATE: Just updated to 4.0.4 and the only thing that was wiped out was the change to /opt/zimbra/conf/postfix_recipient_restrictions.cf. Also, permissions on files created in /opt/zimbra/postfix/conf got changed.)
• This method can be spoofed by forging the MAIL FROM: header (so mail appears to originate from within the domain), so it isn't foolproof, but it works for basic needs.

Steps

• Create a 'permitted senders' list (as user zimbra) - This is your list of domains and/or users who can email your protected email addresses:

vi /opt/zimbra/postfix/conf/permitted_senders

[paste in contents below editing as required]

localhost               OK
mydomain.com            OK
zimbra.mydomain.com     OK
okuser@externaldom.com  OK

• Create a 'protected recipients' list (as user zimbra) - This is your list of email addresses that may only receive email from 'permitted senders'

vi /opt/zimbra/postfix/conf/protected_recipients

[paste in contents below editing as required]

test-dist-list@mydomain.com         permitted_senders_list
protected-user@mydomain.com         permitted_senders_list 

• Create a simple bash script to create postfix DB files (as user zimbra):

vi /opt/zimbra/postfix/conf/update_protected_recipients

[paste in contents below editing as required]

#!/bin/bash
echo "rebuild permitted_senders..."
postmap /opt/zimbra/postfix/conf/permitted_senders
echo "rebuild protected_recipients..."
postmap /opt/zimbra/postfix/conf/protected_recipients

• Make new script executable, then run it

chmod 755 /opt/zimbra/postfix/conf/update_protected_recipients
/opt/zimbra/postfix/conf/update_protected_recipients

• You should now see permitted_senders.db and protected_recipients.db in the directory
• Add necessary settings to /opt/zimbra/postfix/conf/main.cf

vi /opt/zimbra/postfix/conf/main.cf

[add these items to the file - note permitted_senders_list must match value in protected_recipients]

permitted_senders_list = check_sender_access hash:/opt/zimbra/postfix/conf/permitted_senders, reject
smtpd_restriction_classes = permitted_senders_list

• Now add your new restriction to postfix_recipient_restrictions.cf

vi /opt/zimbra/conf/postfix_recipient_restrictions.cf

[paste this into the first line of the file above any other settings]

hash:/opt/zimbra/postfix/conf/protected_recipients

Note 2 from talk: the line to be added to /opt/zimbra/conf/postfix_recipient_restrictions.cf should read:

check_recipient_access hash:/opt/zimbra/postfix/conf/protected_recipients

• Reload postfix to activate settings:

postfix reload

Note 3 from talk: files ownership should be set to root:postfix before reloading postfix. This avoids annoying warning messages in logfile.

Test it out

• Test your settings via telnet:

Enter command:

telnet zimbra.mydomain.com 25

You will see:

Trying 192.168.1.1...
Connected to zimbra.mydomain.com.
Escape character is '^]'.
220 zimbra.mydomain.com ESMTP Postfix

Enter command:

HELO test.com

You will see:

250 zimbra.mydomain.com

Enter command:

MAIL FROM: jdoe@test.com

You will see:

250 Ok

Enter command:

RCPT TO: test-dist-list@mydomain.com

You will see:

554 <test-dist-list@mydomain.com>: Recipient address rejected: Access denied
QUIT
221 Bye
Connection closed by foreign host.

• That's it. If you need to protect new distribution lists or emails, or add new senders, just edit and re-run the update script, then reload postfix.

Additional Resources

Also: http://wiki.zimbra.com/index.php?title=Restrict_sending_to_certain_domains