What I would like to see is something like this.
At the moment PlusNet are just rejecting the messages that are not meeting their criteria.
Why not phase it in? Instead of just introducing hard-blocking based on their own database of IPs.
So instead of just starting to reject the mail (already happened I know)... I would have liked step one to be be to send to the Spam folder any emails that the new system would have dropped, initially.
Then email all customers to tell them you are doing this (and asking them to check their spam folder).
Customers and PlusNet will then be able to see, by the amount more genuine mail going to the Spam folder just how much this is affecting genuine customer mail.
Strkes me that would be a better option (to incorrectly send genuine mail to spam folder) rather than just dropping it. And it would allow PlusNet to see how well the system performs.
With only a small %age of customers using the forums, chances are many more customers may be affected but not know it.
I know other mail providers do the same thing, but something about the PlusNet setup is causing all sorts of issues for customers, clearly. And the problem is, Joe Bloggs hasn't read this thread and doesn't know how to whitelist an IP. He may not even know he is missing email.