Summary
The integration of AMP for email has promised a new era of interactive and dynamic email experiences. However, for some senders, particularly those targeting Outlook inboxes, the reality has been a frustrating increase in spam placement. This often occurs despite the HTML fallback version being sent, suggesting that the mere presence of the AMP MIME part might trigger spam filters.
Key findings
- Outlook compatibility: Outlook.com does not currently render AMP emails, meaning recipients will always see the HTML fallback version.
- MIME part impact: Adding an AMP MIME part, even if Outlook doesn't render it, can negatively affect deliverability of the HTML fallback, potentially increasing spam flagging.
- Deliverability drop: Some senders experience a significant drop in inbox placement (e.g., 10%) when including AMP, even if their fallback HTML is otherwise clean.
- Spam filter sensitivity: Microsoft Exchange Online Protection (EOP) and SpamAssassin can flag AMP emails, indicating heightened sensitivity to this content type.
- Authentication requirements: AMP for email generally requires strong email authentication (SPF, DKIM, DMARC) to be fully passed to avoid deliverability issues.
Key considerations
- Test thoroughly: Conduct A/B tests to compare deliverability of emails with and without the AMP MIME part, specifically for Outlook and other major ISPs. For more information on why emails go to spam, see Mailmodo's guide on common spam reasons.
- Review headers: Examine email headers of AMP emails that land in spam to identify any specific flags or changes that occur during transit, as discussed in our guide on Outlook deliverability issues.
- Sender reputation: Ensure a strong sender reputation, as this is crucial for AMP email acceptance, as highlighted in our related article on AMP code and spam placement.
- Fallback strategy: Optimize your HTML fallback to ensure it is robust and visually appealing, as many recipients (especially Outlook users) will only see this version.
- Authentication protocols: Verify that your SPF, DKIM, and DMARC records are correctly configured and passing for all your sending domains, as this is a prerequisite for AMP success.
What email marketers say
Email marketers often experiment with new technologies like AMP to enhance engagement. However, the practical application can reveal unexpected challenges, particularly with how various email clients and spam filters react to the AMP MIME part. Marketers share experiences ranging from seamless integration to significant deliverability setbacks, even when the AMP content itself isn't rendered by the recipient's client.
Key opinions
- AMP's outlook compatibility: A common understanding among marketers is that Outlook doesn't support AMP, so the fallback HTML version is always displayed.
- Impact on fallback: Even if the AMP part isn't rendered, its mere presence (the AMP MIME part) can cause the fallback HTML to be flagged as spam.
- Deliverability decline: Some marketers have observed a tangible drop in deliverability (e.g., a 10% reduction) when A/B testing emails with AMP versus those without.
- ESP influence: The Email Service Provider (ESP) used can play a role in how AMP emails are handled and their deliverability outcomes.
- Header analysis: Inspecting email headers is a recommended first step to diagnose why emails might be going to spam, as they can reveal processing details.
Key considerations
- A/B testing for impact: Marketers should conduct controlled A/B tests to isolate the impact of AMP on their specific sending practices and audience engagement metrics. This aligns with general best practices for improving email deliverability.
- Monitor deliverability metrics: Regularly monitor inbox placement rates, especially for key domains like Outlook, after implementing AMP emails. Tools and techniques for this are covered in our article on Outlook spam folder issues.
- Examine MIME parts: Pay close attention to how the AMP MIME part is constructed and whether it might be inadvertently affecting the main HTML part's deliverability. Understanding the technical aspects of email structure, such as those described in CXL's guide to AMP for email, can be beneficial.
- Troubleshoot with ESP: If using an ESP, consult their support or documentation regarding AMP email best practices and known deliverability quirks.
- Consider alternatives: If AMP consistently causes issues for Outlook recipients, evaluate if the benefits outweigh the deliverability risks for your specific campaigns.
Marketer view
Email marketer from Email Geeks indicates that they haven't faced any issues with their AMP emails, suggesting that the problem might be specific to how certain senders or ESPs implement AMP. They emphasize the importance of ensuring that the fallback HTML content remains unaffected by the inclusion of AMP.
Marketer view
Email marketer from Email Geeks highlighted a noticeable 10% drop in deliverability observed during A/B tests between a control email and an identical one with an AMP MIME part. This suggests that the presence of AMP, even if not rendered, can have a measurable negative impact on inbox placement.
What the experts say
Experts in email deliverability acknowledge that AMP for email presents unique challenges due to its interactive nature and the varying levels of support from different inbox providers. While AMP aims to enhance user experience, its complex structure and the stringent requirements from providers like Microsoft can inadvertently trigger spam filters, even if the primary issue isn't with the AMP content itself, but its encapsulation.
Key opinions
- Outlook doesn't support AMP: Industry experts confirm that Outlook (including Outlook.com and Exchange Online Protection) does not render AMP content, always falling back to the HTML version.
- Fallback vulnerability: The problem isn't necessarily AMP rendering, but the fact that the presence of the AMP MIME part itself can cause the HTML fallback to be treated as spam.
- Reputation and authentication: Strong sender reputation and robust authentication (SPF, DKIM, DMARC) are critical for AMP emails to pass through filters.
- Content and design factors: Beyond technical setup, the content quality and design of both the AMP and HTML parts play a significant role in avoiding spam classifications.
- Header analysis for diagnostics: Analyzing email headers is key to understanding how filters are processing the message and identifying potential issues.
Key considerations
- Prioritize authentication: Ensure all authentication protocols (SPF, DKIM, DMARC) are correctly implemented and aligned. This is a non-negotiable for AMP. Learn more about DMARC, SPF, and DKIM.
- Monitor specific blocklists: Be aware of any specific blocklists or internal reputation systems used by Microsoft that might penalize AMP content. Understanding how email blacklists work is essential.
- Content quality: Beyond the AMP structure, ensure the content itself is not spammy, misleading, or poorly formatted, as outlined in Netcore Cloud's advice on ensuring inbox delivery.
- Sender behavior: Maintain consistent sending volumes and positive engagement to build and preserve a good sender reputation. Any sudden changes, especially with new content types like AMP, can be scrutinized.
- Monitor spam feedback loops: Register for and actively monitor feedback loops from major ISPs to quickly identify and address spam complaints related to your AMP campaigns.
Expert view
Expert from Email Geeks, tvjames, states that AMP doesn’t work at Outlook, so recipients should always receive the HTML fallback. This implies that any deliverability issues experienced in Outlook are likely related to other factors, not the AMP rendering itself.
Expert view
Expert from Email Geeks, tvjames, explains that tests failing for AMP in Outlook are probably safe, meaning it's an expected behavior since Outlook doesn't support AMP. The concern shifts to why the HTML fallback might be failing.
What the documentation says
Official documentation and industry standards for AMP for email outline specific technical requirements and best practices crucial for deliverability. While the documentation primarily focuses on enabling AMP functionality, it inherently touches upon the security and authentication measures necessary to ensure these dynamic emails are not misidentified as spam by receiving mail servers, including those operated by Microsoft.
Key findings
- Strict authentication: AMP for email requires strong email authentication, specifically DMARC, DKIM, and SPF, to be properly implemented and passed for successful delivery.
- MIME type structure: AMP emails must be structured as multi-part MIME messages, including both the AMP HTML part and a standard HTML or plain text fallback.
- Sender registration: Some inbox providers require senders to register or go through a whitelisting process before they can reliably send AMP emails.
- Security precautions: Email providers often block dynamic content by default to prevent malware, requiring AMP senders to meet high security standards.
- Content validation: AMP content must adhere to specific validation rules and include unique tags like '⚡4email' or 'amp4email' in the HTML.
Key considerations
- Adherence to specifications: Ensure your AMP HTML strictly follows the official AMP for email specifications to avoid validation failures that could trigger spam filters. This includes specific requirements like the proper MIME type.
- Authentication configuration: Verify that your domain's SPF, DKIM, and DMARC records are correctly set up and that your emails consistently pass authentication checks, as detailed in our article on authenticated emails in Outlook junk folders.
- Sender guidelines for outlook: Familiarize yourself with Microsoft's specific sender requirements and guidelines for Outlook.com, especially if sending bulk emails, as these influence deliverability. MarTech provides an overview of new rules.
- Payload size: Be mindful of the overall email size when including both AMP and HTML parts, as excessively large emails can be flagged by spam filters.
- Error handling: Implement robust error handling for your AMP content, ensuring a seamless fallback experience and preventing any malformed AMP from negatively impacting overall deliverability.
Technical article
Documentation from CXL outlines that to send AMP emails, you must provide proof of your sender's reputation and consistently low spam rates to providers like Google and Outlook. Furthermore, senders need to apply and get whitelisted before their first AMP email is accepted, indicating a gatekeeping process.
Technical article
Documentation from AWeber specifies that AMP emails require all authentication settings, including DMARC, DKIM, and SPF, to be passed. This comprehensive authentication is critical because inbox providers scrutinize dynamic content more closely for security reasons.
Related resources
15 resources
Related pages
Can AMP code in emails cause increased spam placement in Outlook and Hotmail, even if they don't render AMP?
Why are my emails having deliverability issues with Microsoft Outlook and Hotmail?
Why are authenticated emails going to junk in Microsoft Outlook?
Why are my emails landing in the spam folder for Outlook and Hotmail?
Why are emails going to spam in Outlook.com?
How to comply with Outlook's new sender requirements
Why your emails are going to spam in 2024 and how to fix it
A simple guide to DMARC, SPF, and DKIM
A practical guide to understanding your email domain reputation
Email Deliverability Issues: Getting Your Messages to the Inbox in 2025
