From around 13:36GMT GlobalNet's (AKAMadasafish) servers have been rejecting forwarded mail:
2010-12-23 15:34:12 1PVlid-0001P6-CG ** REDACTED@@globalnet.co.uk <REDACTED@@example.com> R=nsNaR T=ST: SMTP error from remote mail server after initial connection: host mx-ironport.core.plus.net [84.92.1.97]: 554-mx.ptn-ipin02.plus.net 554 Your access to this mail system has been rejected due to the sending MTA's poor reputation. If you believe that this failure is in error, please contact the intended recipient via alternate means.Unsure why at present, the server is not on any blocklists. The eggheads at Ironport have decided, for reasons only known to them, that one of our servers has a "Poor" reputation. This is based on around two weeks of mail (just a few dozen), none of which were SPAM, as our client confirms. We've been in business for over 13 years BTW.
Solution - we are no longer forwarding mail into PlusNet. Instead we've just finished setting up our affected clients with their very own POP3 mailboxes.