How do SpamAssassin HTML_IMAGE_RATIO scores affect email deliverability and how to diagnose outlook 365 spam issues?

Email marketer from Litmus shares that you can use their tool 'Email on Acid' to preview your email and it runs spam tests using popular filters, including SpamAssassin. Helps give you a heads up of potential problems. It will show you the breakdown on the text vs. image ratio

Email marketer from Mailjet Blog explains that a high image-to-text ratio can negatively affect deliverability. Spam filters may flag emails with excessive images and little text as spam because spammers often use images to bypass text-based spam filters. Maintaining a balanced ratio is important.

Email marketer from an Email Marketing Forum points out that while image ratios and SCL/BCL scores matter, they are just part of a bigger picture. Maintaining a good sender reputation by practicing good email hygiene (list cleaning, engagement tracking, etc.) is essential. Email providers often weigh reputation more heavily than individual email characteristics.

Email marketer from Email Geeks shares that the SpamAssassin HTML_IMAGE_RATIO test is based on the number of images in the email body, and not just the overall size. He advises users to check the total number of images and their impact on image-text ratio

Email marketer from GlockApps Blog shares that using a tool like GlockApps can help pre-test email deliverability and identify SpamAssassin scores before sending emails to a list. This allows marketers to identify and fix issues like high image-to-text ratios or missing authentication records that might trigger spam filters.

Email marketer from Sendinblue Blog shares that balancing images and text is crucial for avoiding spam filters. Providing sufficient text content alongside images helps demonstrate the email's legitimacy and improves sender reputation. It's recommended to use alt text for all images to enhance accessibility and provide context if images don't load.

Email marketer from Reddit recommends analyzing email headers in Outlook 365 to understand why an email was marked as spam. The headers contain information about the email's path, authentication results, and spam filtering decisions made by the email server. Look for SCL scores and other diagnostic information.

Email marketer from Reddit, advises that optimising images by reducing their file sizes can significantly improve deliverability as this helps the emails load faster, which is a positive signal to many email clients. Use image compression tools to reduce the file size without significantly impacting image quality.

Expert from Spamresource.com explains that a high image-to-text ratio in emails can significantly impact deliverability, as spam filters often flag such emails as potential spam. They recommend maintaining a balanced ratio to avoid triggering these filters.

Expert from Word to the Wise, shares that feedback loop (FBL) data gives a lot of information around spam, complaints and deliverability issues. Microsoft provides a SNDS system which contains the data.

Expert from Email Geeks explains that the SpamAssassin score difference of 0.002 between the two emails isn't significant enough to cause deliverability issues, with the email having HTML_IMAGE_RATIO_06 actually having a higher score. Also, she notes that Matt's scores are different than those used by mail-tester.com, indicating that different SpamAssassin installations use different scoring methods, making the SA version used for testing important.

Expert from Email Geeks states that Outlook doesn't use SpamAssassin, so focusing on SpamAssassin scores is not relevant. Instead, she advises to examine the email headers within Outlook 365 to find spam scoring diagnostics and identify the differences between the emails, specifically looking for BCL and SCL scores.

Documentation from Microsoft details Bulk Complaint Level (BCL) thresholds in Microsoft 365. BCL indicates how likely a message is to be a bulk email (newsletter, promotion, etc.). Lower BCLs are considered less likely to be spam. Admins can configure actions based on BCL thresholds, influencing how bulk emails are handled.

Documentation from Microsoft Purview explains to use the Message Header Analyzer tool to examine email headers in detail. This tool can help identify specific spam filtering rules that triggered the spam classification. Access the analyzer in the Security & Compliance Center, submit email headers, and the tool will identify the different header values.

Documentation from Microsoft Learn describes that the Spam Confidence Level (SCL) score in Exchange Online Protection and Outlook indicates the likelihood an email is spam. Higher SCL scores (e.g., 7-9) mean the email is almost certainly spam and will likely be filtered. Analyzing SCL scores in email headers helps diagnose why an email was classified as spam.

Documentation from SpamAssassin Wiki explains that HTML_IMAGE_RATIO tests (e.g., HTML_IMAGE_RATIO_04, HTML_IMAGE_RATIO_06) evaluate the ratio of image area to text area in an HTML email. Higher scores are assigned when the image area is disproportionately large compared to the text, potentially indicating spam. Different ratios trigger different score levels.