It's frustrating to invest time in creating interactive AMP emails, only to find them consistently landing in the spam folder, especially in Outlook. What makes it even more puzzling is that Outlook (and Hotmail) largely stopped supporting AMP for email back in 2020. You'd expect them to simply display the HTML fallback, but sometimes, the mere presence of the AMP MIME part can negatively impact deliverability, even for the fallback version. This can lead to a noticeable drop in your overall email deliverability rates.
This issue points to deeper underlying deliverability problems rather than just an AMP specific glitch. When Outlook flags an email as spam, whether it contains AMP or not, it's usually due to a combination of factors related to your sending reputation, email authentication, and content quality. Let's explore why this happens and what you can do to ensure your emails reach the inbox.
The nuances of AMP and Outlook's mail system
Despite Outlook's official stance on AMP for Email, where they largely ended support, the presence of the AMP MIME part can still sometimes influence how your emails are processed. While the recipient sees the HTML fallback, the email service provider (ESP) still parses the entire message, including the AMP component. If there are any issues with the AMP markup, or if the addition of AMP impacts the email's overall size or complexity, it might trigger spam filters.
Outlook turning off AMP for email means that even if you send a perfectly valid AMP email, it will default to showing the HTML version to Outlook users. However, if your deliverability drops specifically when you include the AMP part, it suggests that Outlook's filters might be applying a stricter scrutiny to multipart messages, or the AMP portion itself, even if not rendered, is seen as a potential risk.
This leads me to believe that while the AMP content isn't being displayed, its presence could still be a red flag. It's crucial to ensure that your AMP markup is clean and valid. Any errors or malformations in the AMP part, even if hidden from the end-user, could contribute to a lower deliverability score from services like Microsoft Exchange Online Protection (EOP). You also need to confirm that your email service provider (ESP) is handling multipart messages correctly, especially when one of those parts is AMP HTML.
Outlook and AMP for email
Limited support: As of early 2020, Outlook (and Hotmail) largely ceased supporting AMP for email. Your recipients will see the HTML fallback.
Processing burden: The email server still processes the AMP MIME part, even if it's not rendered. Any issues with this part could impact deliverability.
Authentication: AMP emails generally require strict authentication to pass, which aligns with Microsoft's increasing demands for sender verification.
Core deliverability factors impacting AMP emails
Even if AMP itself isn't the direct cause, adding it might expose pre-existing deliverability issues. Outlook, like other major inbox providers, heavily relies on sender reputation. This is built over time based on factors such as your sending volume, spam complaint rates, bounce rates, and engagement metrics (opens, clicks, unsubscribes). If your domain or IP has a low reputation, any email, AMP or not, is at risk of being flagged as junk or spam. You can use an email deliverability tester to check for common pitfalls.
Another critical factor is email authentication. SPF, DKIM, and DMARC are fundamental. Microsoft is particularly stringent about these. If your authentication records are misconfigured, incomplete, or failing, your emails will very likely end up in the junk folder, regardless of their content or whether they include AMP. Authenticated emails can still go to junk if other factors are at play, but authentication failures are a primary cause.
Finally, the content of your email itself matters. Even if your AMP part is well-formed, if your HTML fallback contains spammy keywords, suspicious links, or exhibits characteristics of unsolicited bulk mail, it will be flagged. This includes excessive images, poorly formatted HTML, or misleading subject lines. Microsoft's filters are sophisticated and analyze all aspects of an email.
Factor
Positive Impact
Negative Impact
Sender reputation
Consistent sending, low complaints, high engagement.
High spam reports, low engagement, sending to invalid addresses.
Email authentication
Properly configured SPF, DKIM, and DMARC records.
Missing or incorrect authentication records, DMARC failures.
Deep dive into authentication and Microsoft's requirements
For Outlook and other Microsoft properties (Hotmail, Live), email authentication is non-negotiable. They are very strict, and without proper SPF, DKIM, and DMARC alignment, your emails are highly susceptible to landing in the junk folder. This is especially true with recent industry-wide changes by Google and Yahoo, pushing all senders towards stronger authentication.
DMARC is particularly important because it tells receiving servers how to handle emails that fail SPF or DKIM checks. If your DMARC policy is set to p=none, it means you are only monitoring, but not enforcing. To truly protect your domain and improve deliverability, you should aim for a p=quarantine or p=reject policy. This tells Microsoft (and others) to treat unauthenticated emails from your domain with suspicion, often sending them to spam or rejecting them outright. You can use a free DMARC record generator to get started.
If Microsoft Exchange Online Protection (EOP) is assigning a high spam score (like 5.0 in the reported case), it's a clear indicator that your email is failing their checks, likely due to authentication issues or suspicious content. This score signifies a high likelihood of being delivered to the junk folder. Even if the AMP part is not rendered, the overall email structure and authentication integrity are assessed.
Implementing DMARC, along with SPF and DKIM, is essential for demonstrating to Microsoft that your emails are legitimate and from an authorized sender. This significantly reduces the chances of them ending up in the spam folder, whether they are transactional emails, newsletters, or even those containing AMP components.
Troubleshooting and prevention strategies
If you're facing this issue, start by meticulously examining the email headers of a message that landed in spam. Headers contain crucial information about how the email was processed, authenticated, and why it might have been flagged. Look for authentication results (SPF, DKIM, DMARC pass/fail), spam scores, and any specific reasons provided by Microsoft's filters. This will give you concrete clues as to why your AMP (or any) emails are going to junk in Outlook. A drop in deliverability might mean your emails are suddenly going to spam more broadly, not just AMP.
Beyond authentication, actively monitor your sending reputation. Regularly check if your sending IP address or domain is listed on any major blocklists (or blacklists). Being on a blocklist can severely hinder your email deliverability to Outlook users. You can use a blocklist checker for this. Also, ensure your email content is clean, relevant, and avoids common spam triggers. Maintain a healthy list hygiene to minimize bounces and spam complaints.
Given that AMP emails expire and have specific requirements, it's possible that the validation process for AMP is stricter, and any slight deviation could flag the entire email. If you're using an ESP like Klaviyo (as mentioned in the Slack thread), ensure that their AMP implementation is robust and that they handle all aspects of multipart message sending correctly. It is also important to consider if your AMP code in emails can cause increased spam placement even if not rendered.
Ultimately, focus on holistic email deliverability best practices. Strong authentication, consistent positive sender reputation, and clean, engaging content are your best defenses against the spam folder. The AMP component might just be shining a light on existing weaknesses in your email program.
The problem
AMP part triggering filters: Even though Outlook doesn't render AMP, its presence might increase complexity or trigger specific, sometimes undocumented, spam checks. This can lead to your emails landing in Outlook junk folders.
Hidden deliverability issues: The problem often stems from deeper, pre-existing deliverability challenges like poor sender reputation or misconfigured authentication.
ESP handling: Some ESPs might not handle multipart messages with AMP parts optimally, inadvertently causing deliverability issues.
Optimize content: Review your HTML fallback for spam triggers. Ensure clean code and a balanced text-to-image ratio.
Test thoroughly: Use deliverability testing tools to identify specific flags for Outlook or Hotmail (or other Microsoft properties).
Views from the trenches
Best practices
Always include a valid HTML fallback for your AMP emails, as many clients (like Outlook) do not render AMP.
Ensure strong email authentication (SPF, DKIM, DMARC) is in place and correctly configured for your sending domain.
Monitor your domain and IP reputation regularly to catch any issues early and prevent blocklisting.
Maintain a clean email list by removing inactive subscribers and managing bounces effectively to improve engagement.
Common pitfalls
Assuming that if an email client doesn't render AMP, the AMP part has no impact on deliverability.
Ignoring email authentication failures, which are major red flags for Microsoft and other mailbox providers.
Sending to unengaged recipients, which can lead to higher spam complaints and negatively impact sender reputation.
Not thoroughly testing AMP emails across various spam filters and email clients, even for their fallback versions.
Expert tips
If your AMP emails are going to spam, check the raw email headers in Outlook to identify specific spam filter warnings or scores.
A/B test your email campaigns by sending identical HTML versions with and without the AMP MIME part to quantify the deliverability impact.
Ensure your ESP is correctly signing and handling multipart emails, especially those containing AMP HTML.
Focus on the fundamental elements of email deliverability, as the AMP issue might be a symptom of broader reputation or authentication problems.
Expert view
Expert from Email Geeks says AMP generally doesn't work at Outlook, so recipients should always receive the HTML fallback. It is likely safe to assume tests failing there are due to this.
2024-03-30 - Email Geeks
Marketer view
Marketer from Email Geeks says even the fallback (text/html part) gets flagged as spam just by adding an AMP mime part, after testing both fallback-only and fallback + AMP versions.
2024-03-30 - Email Geeks
Summary and final thoughts
While AMP for Email offers exciting possibilities for interactive content, its inconsistent support across email clients, particularly Outlook, can sometimes introduce unexpected deliverability challenges. The core issue of your AMP emails going to spam in Outlook is usually not solely due to the AMP component itself, but rather an amplification of underlying deliverability weaknesses.
Prioritizing robust email authentication (SPF, DKIM, DMARC), maintaining a pristine sender reputation, and ensuring your email content (especially the HTML fallback) is clean and legitimate are paramount. By addressing these foundational elements, you can significantly improve your chances of reaching the inbox, regardless of whether you include AMP components or not. Remember, a healthy email program is your best defense against the spam folder.
Outlook. What makes it even more puzzling is that Outlook (and Hotmail) largely stopped supporting AMP for email back in 2020. You'd expect them to simply display the HTML fallback, but sometimes, the mere presence of the AMP MIME part can negatively impact deliverability, even for the fallback version. This can lead to a noticeable drop in your overall email deliverability rates.
Outlook's filters might be applying a stricter scrutiny to multipart messages, or the AMP portion itself, even if not rendered, is seen as a potential risk.
