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Cloudmark Cartridge Installation and Administration Guide Chapter 5
24 Header whitelisting
Following are example configurations that allow mail from hosts with the
specified IP addresses to bypass spam-filtering:
type=host; address=[1.2.3.4]
type=host; address=[1.2.3]
type=host; address = [192.168.32.0/24];
In the first example, only mail from the host at the exact IP address bypasses
spam filtering. The second example allows mail to bypass spam-filtering if only
the first three octets of the IP address match. The third example shows an entry in
CIDR format.
! A CIDR mask of /0 is invalid.
In the case of hostname whitelisting, a domain suffix match will be performed to
determine if an email should bypass spam filtering. Here is an example:
type=host; address=[bar.com]
In this case, if the server’s IP address resolves to bar.com or anything.bar.com, the
email will bypass the spam filter. As long as there is an exact match on the right
side of the hostname, then the email will be whitelisted.
! It is important to understand that host whitelisting does not make use of regular
expressions. The matches must be exact prefix matches in the case of IP addresses
and exact suffix matches in the case of hostnames.
Header whitelisting
Header whitelisting checks the header fields of incoming mail. The header
whitelist value is a regular expression that is applied to the whole header.
Header whitelisting is not foolproof, because spammers sometimes forge (or
“spoof”) header information. Additionally, a header may be added to a spam
message when it is relayed by a trusted host and could then be passed to the
recipient without being scanned for spam.