We cannot detect why it is spam. I did a quick search engine check for some third-party tools (there are many) . I copied URLs of a few that I share here. Spam can be due to bad IP address, insecure setup of server (DKIM and SPF records(, and often relaying (using one email address for message and another one for SMTP). These may help: https://inboxlane.com/email-spam-test.php https://mxtoolbox.com/blacklists.aspx https://mailchecker.net/