Yesterday Spamhaus decided to block a whole 254 address range of IP addresses, owned by Netrino who host my server, because they didn't consider that Netrino had taken suitable action against a spammer.
Today they have relented a little, and only a 16 address range is now being blocked. So e-mail from hundreds of innocent businesses is now able to flow a little better again.
It would have been nice if Spamhaus had done a little more homework before blocking such a large range of addresses. The addresses clearly come from a server hosting company, with only a few IPs allocated to each of their customers.
At least it has prompted me to find out how to relay outbound e-mail via my other server, hosted by Clustered.net. This worked fine while it was needed, and I've updated all my customers' SPF records to allow either server to send out mail for their domains. MailScanner's watermarking also proved useful in this situation, as each message only needed to be scanned by one of the servers.
So while Spamhaus' bullying action certainly annoyed, it has resulted in a little more resilience against potential spam blacklisting for Fonant e-mail services if this sort of thing ever happens again.