Our message check system is based on Spam Assassin which is only used by a few email systems. These message check features are not the same antispam filters that major ISPs use such as AOL, YAHOO, GMAIL, HOTMAIL, etc.
SpamAssassin is an open-source, content-matching spam filter from the Apache Software Foundation. SpamAssassin uses several different filtering techniques to catch spam, including DNS blocklists, text analysis, Bayesian filtering, and collaborative filtering databases.
It uses a scoring system and plug-ins to analyze your email header and the email body copy. The filter then produces a header that outlines your SpamAssassin score and how your email performed against its various checks.
SpamAssassin will provide you with a breakdown of the score. The more items in the message that trigger the SpamAssassin ruleset, the higher the spam score will be.
Unfortunately, there is no available SpamAssassin ruleset information and solutions out there that we can use to fix the errors identified by their system.
Generally, your email should have a score of 5.0 or lower to be considered passing.