Customized spam score for RBL listed senders

Revision as of 07:06, 28 July 2020 by Rnoti (talk | contribs) (Customized spam score for RBL listed Senders)

Customized spam score for RBL listed Senders


   KB 24126        Last updated on 2020-07-28  




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Requirement

Add positive/negative spam score to the email if senders IP listed in the RBL's.

Description

RBL's will work at the MTA (postfix) level, so if sender IP is listed in the RBL then the email is rejected by MTA (where RBL's enabled) without any notification. To allow email without compromising security check, disable RBL check at MTA level and enable at Amavis level (Spam assassin).

Steps to follow

Step-1
  • Remove required RBL's at MTA level if enabled.
Note: If RBL's not enabled at MTA level then this step can be skipped.
  • Global level configuration.
    zmprov mcf -zimbraMtaRestriction "reject_rbl_client <RBL Address>"
i.e.:
zmprov mcf -zimbraMtaRestriction "reject_rbl_client xbl.spamhaus.org"
  • Server level configuration
    zmprov ms `zmhostname` -zimbraMtaRestriction "reject_rbl_client <RBL Address>"
Step-2
  • Edit spam assassin configuration file and add lines in below syntax for RBL lookup.
# /opt/zimbra/conf/salocal.cf.in
header CUSTOM_LOOKUP eval:check_rbl('zen','zen.spamhaus.org.')
describe CUSTOM_LOOKUP Entries listed in zen.spamhaus.org RBL
score CUSTOM_LOOKUP 2.0
Note: CUSTOM_LOOKUP is a key for this definition so keep this same for every line. 2.0 is a positive SPAM score, to give negative spam score use -2.0.
i.e.:
# Rule -1:
header CUSTOM_LOOKUP_5 eval:check_rbl('spam','spam.dnsbl.sorbs.net.')
describe CUSTOM_LOOKUP_5 Entries listed in spam.dnsbl.sorbs.net RBL
score CUSTOM_LOOKUP_5 2.0
# Rule -2:
header CUSTOM_LOOKUP_6 eval:check_rbl('recent','recent.spam.dnsbl.sorbs.net.')
describe CUSTOM_LOOKUP_6 Entries listed in recent.dnsbl.sorbs.net RBL
score CUSTOM_LOOKUP_6 2.0
Step-3
  • Restart Amavisd, MTA services.
zmamavisdctl restart
zmmtactl restart

Validation

The below is a sample message header when the sender IP is RBL listed.

X-Spam-Status: No, score=3.451 required=6 tests=[CUSTOM_LOOKUP_5=2, CUSTOM_LOOKUP_6=2, DKIM_SIGNED=0.1, DKIM_VALID=-0.1]


Submitted by: Raghu Noti
Verified Against: ZCS 8.8.15, ZCS 9.0 Date Created: 2020-07-28
Article ID: https://wiki.zimbra.com/index.php?title=Customized_spam_score_for_RBL_listed_senders Date Modified: 2020-07-28



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