Why are my emails being marked as spam even with good domain reputation?
Summary
What email marketers say7Marketer opinions
Email marketer from HubSpot says gradually increasing the volume of emails sent from a new IP address to build a sending reputation is a vital step to ensure deliverability to the inbox instead of the spam folder.
Email marketer from Email Marketing Forum explains that a high complaint rate (even a small percentage) can override a good domain reputation. ISPs prioritize user experience and will filter emails reported as spam.
Email marketer from Reddit suggests that using a shared IP address can lead to deliverability issues if other users on the same IP are sending spam, even if your domain reputation is good. Recommends considering a dedicated IP address.
Email marketer from Litmus shares that poor list hygiene, including sending to inactive or invalid email addresses, can negatively impact sender reputation and lead to emails being marked as spam. They emphasize the importance of regularly cleaning email lists.
Email marketer from SendGrid Blog explains that certain keywords, phrases, or HTML code in the email content can trigger spam filters, regardless of the sender's reputation. They advise avoiding spam trigger words and ensuring clean, well-formatted HTML.
Email marketer from Mailchimp Resource Center shares that engagement metrics like open rates, click-through rates, and spam complaints significantly impact deliverability. Even with a good sending reputation, low engagement can lead to emails being marked as spam.
Email marketer from ActiveCampaign suggests that having properly configured SPF, DKIM, and DMARC records are necessary to ensure your emails aren't marked as spam. A DMARC policy tells receiving mail servers what to do with messages that fail authentication checks.
What the experts say5Expert opinions
Expert from Email Geeks explains that low bounce rates could be due to bounce handling and lack of complaints could be due to sending primarily to Gmail/business domains or mail going to the bulk folder. If seeing spam placement for probe addresses, there is likely a problem with permission, and addresses are receiving mail without signing up.
Expert from Word to the Wise explains that complaints drive a lot of filtering decisions. Even if your technical setup (authentication, IP reputation) is perfect, a high complaint rate can still cause your emails to go to the spam folder.
Expert from Spam Resource explains that ISPs filter mail based on what their customers want. A sender might have a good reputation overall, but if enough recipients mark their mail as spam, it will be filtered for others on that ISP.
Expert from Email Geeks clarifies that Cloudmark acquired Vipul and runs the hash server for Razor. He also explains that spammy content can be detected by various heuristics, but it doesn't necessarily imply data sharing or code commonality.
Expert from Email Geeks explains that Razor2 is unlikely to be causing delivery problems at Gmail and Microsoft, but the issues that cause listing on Razor2 may also be considered by Gmail and Microsoft.
What the documentation says4Technical articles
Documentation from Google Workspace Admin Help explains that Gmail filters spam based on many factors, including sender authentication (SPF, DKIM, DMARC), user reports, and content. Good domain reputation is important, but not the only factor. They recommend reviewing their bulk sender guidelines.
Documentation from RFC answers details how the DMARC record in DNS allows senders to indicate that their messages are protected by SPF and/or DKIM, and gives instructions to receivers if neither of those authentication methods pass.
Documentation from Spamhaus explains that being listed on their blocklists is a common reason for emails being marked as spam. Blocklisting can occur even with good domain reputation if the sender's IP address or domain has been associated with spam activity, even unintentionally (e.g., compromised server).
Documentation from Microsoft Learn shares that Outlook uses the SmartScreen Filter, which learns from user feedback to identify spam. Even with good domain reputation, individual emails can be marked as spam if they trigger the filter's heuristics or are reported as spam by recipients.