RCVD_IN_PBL gets triggered on local email

[Deeztek Support via amavis-users]

I noticed that if I add a domain ex: @mydomain.tld in the users table in 
amavis, e-mail originating from a user from that domain gets blocked as 
spam and quarantined by amavis. The culprit seems to be
RCVD_IN_PBL. After some research I found that this may be caused by the 
fact that authentication is missing. This only happens from emails 
originating from the Exchange Server. If I add a domain from a 
non-exchange server in the users table, it passes clean presumably 
because the non-exchange e-mail uses sasl authentication where the 
Exchange server obviously does not.

Any ideas?
Thanks

Dino