This puzzled me. We have all mail directed to an ISP's spam filter, then delivered to SBS 2008 Exchange. One of the ISP's IP numbers suddenly appeared in the ES2007 block list, set to expire in 24 hours I think, so emails started bouncing.
Quick look through the typically ponderous docs, and I can't see anything that says Exchange will auto-block an IP number, but nobody is admitting to adding it manually and I think it must have done.
Anyone know about this or where it is configured? Obviously one could disable block lists completely but I'd like to know exactly why this happened.