Spamassassin & dnsbl questions

[Rasmus Haslund]

Hi,
 
Sorry if this seems like a stupid question but I am just trying to
understand the config files better.
 
For example these:
 
header __RCVD_IN_NJABL  eval:check_rbl('njabl', 'combined.njabl.org.')
describe __RCVD_IN_NJABL Received via a relay in combined.njabl.org
tflags __RCVD_IN_NJABL  net
 
header RCVD_IN_NJABL_RELAY eval:check_rbl_sub('njabl', '127.0.0.2')
describe RCVD_IN_NJABL_RELAY NJABL: sender is confirmed open relay
tflags RCVD_IN_NJABL_RELAY net

In the header area there is a __ infront of one rule but not the
other... is this just naming or does it have any special meaning?
For example i am thinking this could be a way to check not just the last
hop before our mailserver but im not sure and 
http://wiki.apache.org/spamassassin/DnsBlocklists doesnt seem  to
provide an explanation on this.
 
Thank you in advance.
 
Best Regards
 
 
Rasmus Haslund
 
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