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It is the best route to go for a specific issue like this, as they can look into your VPS and provide customized suggestions about your specific issues.
Based on the information you provided, here's a sample spam report:
Essentially your outgoing email scores over 5 in SpamAssassin, which is the threshold for "Spam". As you can understand, we do not want to be labeled as a spam source on the internet, so we do what we can to sanitize outgoing email. It is in our best interest and the best interest of our customers.
X-Spam-Status: Yes, score=6.7 required=5.0 tests=BAYES_40,FSL_HELO_NON_FQDN_1,
* 0.0 FSL_HELO_NON_FQDN_1 FSL_HELO_NON_FQDN_1
* -0.0 BAYES_40 BODY: Bayes spam probability is 20 to 40%
* [score: 0.2662]
* 0.0 HTML_MESSAGE BODY: HTML included in message
* 0.7 MIME_HTML_ONLY BODY: Message only has text/html MIME parts
* 0.5 MISSING_MID Missing Message-Id: header
* 0.8 RDNS_NONE Delivered to internal network by a host with no rDNS
* 0.0 HELO_NO_DOMAIN Relay reports its domain incorrectly
* 0.4 HTML_MIME_NO_HTML_TAG HTML-only message, but there is no HTML tag
* 0.0 TVD_SPACE_RATIO TVD_SPACE_RATIO
* 3.2 TO_EQ_FM_HTML_DIRECT To == From and HTML only, direct-to-MX
* 1.1 TO_EQ_FM_DIRECT_MX To == From and direct-to-MX
Please contact our Customer Support team and they will be more than happy to assist you further.