How to check why a outbound message is identified as spam?

Hello!

I have trouble checking an outbound message misidentified as spam.

This is a legitimate email (this is a response email in html, with many footers but without attachment).

I send this email marked as "This is NOT SPAM" to Symantec Security Response from Message Quarantine, but is nothing better.

How to check, what is the reason of mark this email as spam?

Thanks a lot!