strange delivery error message - blocked by ldap?   

all emails sent to comcast.net were being blocked, I kept getting the ndrs 
that said:

ourmailserver #5.5.0 smtp;550-xx.xxx.xxx.xx blocked by 
ldap:ou=rblmx,dc=comcast,dc=net>


I have a smarthost configured for domains that block our IP, once I 
configured all emails to comcast to go thru the smarthost everything went 
thru, but I am just confused as to the ldap error.  can somebody explain 
this to me?

date: Sun, 23 Apr 2006 10:57:17 -0400   author:   Gary Massengale