Your message very likely looks like spam and you are getting a false positive. The best would be to check the 'spamminess' of your e-mail using Mail Tester.
Indeed, this free service is literally for testing the 'spamminess' of your e-mails and avoid false positives. You just need to send your message to an e-mail address they will give you. A few seconds later you will get a score and a detailed report of what is ok and what is wrong. That simple! In addition, you get some directions to fix the problems. The best here is to try to get a score of 10/10.
MaxBulk Mailer is a full-featured and easy-to-use bulk mailer and mail-merge software for macOS and Windows that allows you to send out customized press releases, prices lists, newsletters and any kind of text or HTML documents to your customers or contacts.
MaxBulk Mailer is fast, fully customizable and very easy to use. MaxBulk Mailer handles plain text, HTML and rich text documents and gives full support for attachments. With MaxBulk Mailer you will create, manage and send your own powerful, personalized marketing message to your customers and potential customers.
Thanks to its advanced mail-merge and conditional functions you can send highly customized messages and get the best results of your campaigns. You also have support for international characters, a straightforward account manager with support for all type of authentication schemes including SSL, a complete and versatile list manager, support for importation from a wide range of sources including from remote mySQL and postgreSQL databases.
MaxBulk Mailer is a software tool that you purchase once, no need to pay on a per-email basis to submission services!