Just a heads up, I'm not getting any of my mail for my domain that is forwarded by 1st domains. I've opened a support ticket with them and will see what happens.
Details below slightly changed (email addresses)...
Reporting-MTA: dns; omr2.mail.isx.net.nz
X-Postfix-Queue-ID: 78870935AF3
X-Postfix-Sender: rfc822; someuser@gmail.com
Arrival-Date: Tue, 15 Jan 2013 09:51:50 +1300 (NZDT)
Final-Recipient: rfc822; auser@xnet.co.nz
Original-Recipient: rfc822;dan@1stdomainsredirectdemail.co.nz
Action: failed
Status: 5.7.1
Remote-MTA: dns; mx1.xnet.co.nz
Diagnostic-Code: smtp; 554 5.7.1 Service unavailable; Client host
[111.65.230.131] blocked using b.barracudacentral.org;
http://www.barracudanetworks.com/reputation/?pr=1&ip=111.65.230.131