What causes Apple's policy-related (CS01) bounce messages and how can I resolve them?
Summary
What email marketers say12Marketer opinions
Email marketer from MailerMailer shares some common reasons behind policy related bounces and what you can do to help solve them. This includes, authenticating your emails, cleaning your email lists and ensuring your content is relevant to the recipients.
Email marketer from Reddit says bounce issues could be related to content. MailerDaemon suggests analyzing the content and subject lines of emails that are bouncing. They recommend to avoid spam trigger words and phrases and also not use excessive formatting or images.
Email marketer from Email Geeks explains that CS01 is primarily content based, and asks if Chris has tried to reach out to them as the apple team tends to review things.
Email marketer from EmailToolTester shares some tips to help increase email deliverability. This includes properly setting up authentication (SPF, DKIM, DMARC), keeping your lists clean and up to date, warming up your IPs and choosing the right sending software.
Email marketer from Stack Overflow suggests that CS01 errors often relate to content issues, specifically links to questionable sites. They recommend reviewing the content for potentially problematic links and also suggest checking the sender's reputation and authentication setup.
Email marketer from Email Geeks shares that assuming you’re sending from the same IP / sending domain and only seeing intermittent issues, she would rule out authentication. So in that case, it would be reputation related. She suggests checking if the occurences line up with volume spikes, as there’s probably an influx of less engaged subscribers being included in the volume spikes that are probably spiking your “mark as spam” counts and to check if your IP is listed on SORBS, as she has been hearing of a few instances where SORBS listings are impacting iCloud filtering.
Email marketer from Gmass shares some ways to improve sender reputation which includes: authenticating your emails, keeping spam complaints low, clean your email lists, send engaging emails, and maintain a consistent sending volume.
Email marketer from CampaignMonitor shares some reasons for bounces which include: a full inbox, server down, or a general block.
Email marketer from Email Hippo explains some general ways to avoid blocks from mail providers which include: using dedicated IPs, using double opt in, segmenting lists, cleaning lists, and being careful not to send too frequently.
Email marketer from Email Geeks adds that if you can get hold of a header that was filtered you can usually see their spam scores listed within the header. That might give you additional insight into what is causing the issue.
Email marketer from Reddit suggests that iCloud's filtering is sensitive. The user states that it's important to make sure the sender's IP isn't on any blacklists and that the sending domain has a solid reputation. They say warming up IPs gradually can help to reduce bounce errors.
Email marketer from GlockApps shares some content best practices. This includes, avoiding misleading subject lines, make sure links are relevant, include a physical address and don't send only images.
What the experts say2Expert opinions
Expert from Word to the Wise, Laura Atkins, shares that CS01 errors often relate to content, including URLs within the email. She recommends analyzing the URLs included in the email to make sure that the links are not blacklisted or have a bad reputation. She also suggests using URL shorteners in moderation, because excessive use of them can get you flagged.
Expert from Spamresource explains some reasons to why your email is being blocked. The article goes on to state that to help prevent this, ensure that your sending IP is not on any blacklists, authenticate emails correctly and monitor spam complaints.
What the documentation says4Technical articles
Documentation from RFC explains the meaning of SMTP enhanced status codes. While it doesn't address CS01 specifically, it explains the structure of these codes, indicating that 5.7.1 generally refers to delivery policy violation. This suggests the receiving server's policy (likely content or reputation-based) is the cause.
Documentation from SendGrid explains the difference between hard and soft bounces. Hard bounces are permanent reasons that an email cannot be delivered (like the email doesnt exist), where as soft bounces are temporary (full inbox for example).
Documentation from Apple Support explains that bounce messages, including those related to policy rejections, indicate issues with the email delivery process. While they don't specifically detail CS01, they recommend checking the sender's email authentication settings (SPF, DKIM, DMARC) and ensuring the sending domain has a positive reputation. They also suggest reviewing email content for anything that might be flagged as spam.
Documentation from SparkPost shares that CS01, or similar policy-related rejections indicate the receiving server has identified the email as violating its policies. They advise reviewing sending practices, content, and authentication settings and ensuring compliance with email best practices, and checking blacklists.