Quoting Daniel Carrera daniel.carrera@theingots.org:
Btw, we currently use Mailfoundry as our spam filter, and Mailfoundry also has problems red-listing the IP of the school in question. It's the same reason - a large number of emails originating from this IP are interpreted as spam.
Is there some means for you to verify that it isn't SPAM? Is it possible to white list the IP address? Are there controls at the school to prevent its servers from being used by external users/servers for Relay, etc.? If the school's servers aren't sound then they should get that fixed. If someone in the school is abusing the schools services they should get that fixed.
-- Earnie