MadridMan,

I know that I am really late to this thread, but as an FYI it might be relevant for the future.

The reason your emails are getting rejected is because you possibly do not have a reverse DNS record for your own mail server. A common symptom of a spamming mail server is one that has no reverse record, because the server will only exist for a short period of time so they don't register it. The downside is that any legitimate mail servers that fall into this bucket also get rejected.

HTH,
Daniel