Not sure if this is the right forum....
I set my parents up on talktalk e-mail last weekend (they've just gone onto broadband, finally!), when they e-mail me they get the following bounce back (as does another TalkTalk user). I can't decide if it's our server bouncing them or TalkTalk not liking us! I have recently added RBLs to our Exchange Server and have seen a reduction in Spam (we use Sophos Puremessage as well) so am reluctant to take them off.....
Reporting-MTA: dns; ttsmtp.cpwnetworks.com
Status: 5.0.0 (permanent failure)
Remote-MTA: dns; [212.xxx.235.xxx]
Diagnostic-Code: smtp; 5.1.0 - Unknown address error 550-'5.7.1 Recipient not authorized, your IP has been found on a block list' (delivery attempts: 0)