[Mimedefang] rbl checks

[Bill Friedman]

The documentation says rbl checking is enabled by default.  I don't know 
if I somehow deselected that option during some point in the 
installation or not, but, now that I see where it's set in 
sa-mimedefang.cf, I'm curious just how it works.  Thanks for any info.

# By default, SpamAssassin will run RBL checks.  If your ISP already
# does this, set this to 1.

skip_rbl_checks 0