CWL and CBL
Table of content
Description
The Custom Black List (CBL) and Custom White List (CWL) are per-recipient-domain black-/ or whitelists. This is basically a re-implementation of postfix built in smtpd_restriction_classes. If you prefer those, use them! There are various use cases which require those kind of recipient domain based black-/whitelists. If you can't think of any (eg if you run a mail server for your company with only "global" black-/whitelists) you probably don't need them.
Configuration
use_negative_cache
Default: 0
Allowed values: 0, 1
Cache entries for database misses will be written, too. Depending on the kind of SPAM you receive, it might fill your cache very fast (and triggers invalidation far to early) or not.
tables
Default: empty
Allowed values: array of [ 'ips', 'domains', 'addresses' ]
There are three kind of tables which could be used for lookups:
- ips
Maps IP addresses to recipient domains.- Use case CBL: The holder of the domain recipient.tld does not want to receive any mails from the mail server with the IP 123.123.123.123.
- Use case CWL: The holder of the domain recipient.tld is in a business relationship with a company whose mailserver has the IP 123.123.123.123 and wants to assure all mails from them come through.
- domains
More dangerous than IPs, because recipients are arbitrary forgeable.- Use case CBL: The holder of the domain recipient.tld does not want to receive any mails from badpeople.tld.
- Use case CWL: The holder of the domain recipient.tld is in a business relationship with a company whose domain is goodpeople.tld and wants to assure all mails from them come through, even though there might be some forged mails.
- addresses
- Use case CBL: The holder of the domain recipient.tld does not want to receive any mails from the sender someone@badperson.tld.
- Use case CWL: The holder of the domain recipient.tld is in a business relationship with user@goodperson.tld and wants to assure all mails from him come through, even though there might be some forged mails.
Usage Suggestion
Put the CWL in front of the CBL and DNSBL. The CBL can be used before or after DNSBL, but for the it is faster than DNSBL (no name resolution and probably small dataset), so better before DNSBL.
Database
This module uses the database. Here is the SQL example for creating the tables. It is written in SQLite, but should be usable with small or no modifications in most supported RDBS.
CBL
-- TABLE: cbl_domains (SQLITE):
CREATE TABLE CBL_DOMAINS (sender_domain varchar(255), recipient_domain varchar(255),
id INTEGER PRIMARY KEY);
CREATE UNIQUE INDEX CBL_DOMAINS_RECIPIENT_DOMAIN_SENDER_DOMAIN
ON CBL_DOMAINS (recipient_domain, sender_domain);
-- TABLE: cbl_addresses (SQLITE):
CREATE TABLE CBL_ADDRESSES (sender_address varchar(255), recipient_domain varchar(255),
id INTEGER PRIMARY KEY);
CREATE UNIQUE INDEX CBL_ADDRESSES_RECIPIENT_DOMAIN_SENDER_ADDRESS ON CBL_ADDRESSES
(recipient_domain, sender_address);
-- TABLE: cbl_ips (SQLITE):
CREATE TABLE CBL_IPS (client_address varchar(39), recipient_domain varchar(255),
id INTEGER PRIMARY KEY);
CREATE UNIQUE INDEX CBL_IPS_RECIPIENT_DOMAIN_CLIENT_ADDRESS ON CBL_IPS (recipient_domain,
client_address);
CWL
-- TABLE: cwl_domains (SQLITE):
CREATE TABLE CWL_DOMAINS (sender_domain varchar(255), recipient_domain varchar(255),
id INTEGER PRIMARY KEY);
CREATE UNIQUE INDEX CWL_DOMAINS_RECIPIENT_DOMAIN_SENDER_DOMAIN ON CWL_DOMAINS
(recipient_domain, sender_domain);
-- TABLE: cwl_addresses (SQLITE):
CREATE TABLE CWL_ADDRESSES (sender_address varchar(255), recipient_domain varchar(255),
id INTEGER PRIMARY KEY);
CREATE UNIQUE INDEX CWL_ADDRESSES_RECIPIENT_DOMAIN_SENDER_ADDRESS ON CWL_ADDRESSES
(recipient_domain, sender_address);
-- TABLE: cwl_ips (SQLITE):
CREATE TABLE CWL_IPS (client_address varchar(39), recipient_domain varchar(255),
id INTEGER PRIMARY KEY);
CREATE UNIQUE INDEX CWL_IPS_RECIPIENT_DOMAIN_CLIENT_ADDRESS ON CWL_IPS (recipient_domain,
client_address);
Example
For CBL and CWL alike
---
disable: 0
use_negative_cache: 1
tables:
- ips
- domains
- addresses
Performance
Depending on your database, but should be very fast.