One possibility could be to install SpamAssassin on the server and run it through this installation.
Is there some online service where I can paste/send the mail to and this service gives me the SPAM headers?
Yes, I know that you can configure SpamAssassin with different settings and therefore the SPAM score may vary from installation to installation, but a basic evaluation would help already.
Or is there a possibility to check the RFC conformance of a message? (Because SpamAssassin also evaluates this (eg. MIME_HTML_ONLY which means that you have no plain text content and therefore the mail isn't RFC conformant)).
Thanks!!
Solution
Here are some online resources for checking spam scores: