Rejecting false "mail from" addresses: Difference between revisions
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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. | 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. | ||
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: Whenever an SMTP transaction is used to send a DSN, the MAIL FROM command MUST use a | : Whenever an SMTP transaction is used to send a DSN, the MAIL FROM command MUST use a | ||
: NULL return address, i.e., "MAIL FROM:<>". | : NULL return address, i.e., "MAIL FROM:<>". | ||
'''If you want to Enforce a match between FROM addres and SASL username, use the next Wiki for Zimbra Collaboration 8.5 and above: https://wiki.zimbra.com/wiki/Enforcing_a_match_between_FROM_address_and_sasl_username_8.5''' | |||
{{Article Footer|Zimbra Collaboration 8.0, 7.0|04/16/2014}} | {{Article Footer|Zimbra Collaboration 8.0, 7.0|04/16/2014}} |
Revision as of 11:23, 15 July 2015
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.
1. 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. [This steps is for ZCS 7.x and older version only].
su - zimbra zmlocalconfig -e postfix_smtpd_sender_restrictions="reject_unknown_sender_domain, permit_mynetworks, permit_sasl_authenticated, check_sender_access hash:/opt/zimbra/conf/domainrestrict, permit"
For ZCS 8.0.x, open the file /opt/zimbra/conf/zmconfigd/smtpd_sender_restrictions.cf and add this line into the middle of the file, prior to the tag_as_foreign.re lines:
Add this:
check_sender_access hash:/opt/zimbra/conf/domainrestrict
Here:
... check_sender_access hash:/opt/zimbra/conf/domainrestrict %%contains VAR:zimbraServiceEnabled antivirus^ check_sender_access regexp:/opt/zimbra/postfix/conf/tag_as_foreign.re%%
Remaining steps are same for all versions prior to ZCS 8.5.
2. Create the file "/opt/zimbra/conf/domainrestrict" 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!
3. Create the hash database of "/opt/zimbra/conf/domainrestrict". Run as 'zimbra' user.
postmap /opt/zimbra/conf/domainrestrict
4. Restart zmmtactl.
zmmtactl stop zmmtactl start
Testing
Make following connection from a non-local host which is not part of mynetworks.
telnet ZCS_server_address 25 mail from: user@localdomain.com rcpt to: user2@localdomain.com
You should get following error at the rcpt command.
554 5.7.1 <user@localdomain.com>: Sender address rejected: You're not me!
Special case of empty 'mail from' address
Emails can still be sent if the 'mail from:' address is blank, but the 'from' address is specified in the body of the email. This is expected behaviour, and is required by RFC 3464:
- The From field of the message header of the DSN SHOULD contain the address of a human who
- is responsible for maintaining the mail system at the Reporting MTA site (e.g., Postmaster), so that
- a reply to the DSN will reach that person.
- ...
- Whenever an SMTP transaction is used to send a DSN, the MAIL FROM command MUST use a
- NULL return address, i.e., "MAIL FROM:<>".
If you want to Enforce a match between FROM addres and SASL username, use the next Wiki for Zimbra Collaboration 8.5 and above: https://wiki.zimbra.com/wiki/Enforcing_a_match_between_FROM_address_and_sasl_username_8.5