As far as the best way to stop yourself getting blocked by IronPort
Reputation, it's actually quite easy - Don't send spam! Once you take
out the concepts that most anti-spam products use such as dynamic IP
lists/etc, the vast majority of the factors used to calculate your
reputation are based on the volume of spam seen, both by other
IronPorts as well as various spamtraps.

Now that's a funny one Scott. As someone who has controlled the particular IP of his smtp server for 5+ years, I can say without doubt that it hasn't sent spam in at least that long. And we were an early adopter of SPF. None the less, end users of certain ISPs don't get our email. What to do? Obviously with fewer than 20 accounts we're not going to build up a positive reputation in the world of email. Does that mean we're spammers? No. Do I feel blackmailed into paying my way out of this situation? Not yet, but getting there.