Why is my email deliverability to Microsoft Outlook and Hotmail so bad?

Summary

Poor email deliverability to Microsoft Outlook and Hotmail is a multifaceted problem stemming from issues with sender reputation, authentication, list hygiene, content, sending practices, and Microsoft's specific policies. A key factor is Microsoft's heavy reliance on sender reputation, influenced by IP/domain reputation, user engagement, and complaint rates. Authentication is crucial, with Microsoft prioritizing senders using SPF, DKIM, and DMARC. List hygiene is also critical, as sending to outdated or unengaged addresses leads to bounces and complaints. Content that triggers spam filters negatively impacts deliverability. Microsoft implements strict throttling policies and considers volume changes carefully. Shared IPs with poor reputations, and the lack of consistent sending patterns contribute to the issue. Monitoring blocklists, using SNDS, implementing feedback loops, warming up new IPs, A/B testing, and ensuring a properly configured reverse DNS record are vital for improving deliverability. Additionally, it's important to note that Outlook.com and Office365 may require slightly different strategies.

Key findings

  • Sender Reputation: Microsoft prioritizes sender reputation (IP, domain, engagement) when filtering emails.
  • Authentication: Proper SPF, DKIM, and DMARC authentication is essential.
  • List Hygiene: Poor list hygiene leads to bounces and complaints.
  • Content Quality: Spam triggers in content negatively impact deliverability.
  • Throttling Policies: Microsoft implements strict throttling, especially for new IPs.
  • Volume Sensitivity: Microsoft is sensitive to sudden changes in sending volume.
  • Shared IP Risks: Shared IPs can suffer from the poor practices of other senders.
  • Engagement: Low engagement signals unwanted email.
  • Blocklist Impact: Being on a blocklist significantly impacts deliverability.
  • Separate Platforms: Outlook.com and Office365 can behave differently.

Key considerations

  • Monitor Reputation: Actively monitor your sender reputation using SNDS and other tools.
  • Implement Authentication: Ensure correct SPF, DKIM, and DMARC configuration.
  • Practice List Hygiene: Regularly clean your email lists.
  • Improve Content: Avoid spam trigger words and ensure proper formatting.
  • Warming Process: Gradually warm up new IPs.
  • Consistent Volume: Maintain consistent sending volumes.
  • Blocklist Monitoring: Actively check and address blocklist listings.
  • Utilize SNDS: Regularly check and analyze the SNDS data.
  • Implement FBL: Set up a Feedback Loop to handle complaints.
  • rDNS Configuration: Ensure your reverse DNS record is correctly configured.
  • A/B Testing: Perform A/B Testing to improve deliverability.
  • Encourage Engagement: Encourage opens/clicks and get your users to move you from the junk folder or add to safe senders list.

What email marketers say
14Marketer opinions

Poor email deliverability to Microsoft Outlook and Hotmail is often attributed to a combination of factors related to sender reputation, authentication, list hygiene, content quality, and sending practices. Microsoft places a strong emphasis on sender reputation, which is affected by complaint rates, engagement metrics, and IP/domain history. Inconsistent sending volumes, shared IPs with poor reputations, and lack of proper email authentication (SPF, DKIM, DMARC) can negatively impact deliverability. Furthermore, content that triggers spam filters, poor list hygiene, and lack of user engagement contribute to the problem. Warming up IPs, consistent sending volumes and using A/B testing also improve deliverability.

Key opinions

  • Sender Reputation: Microsoft heavily relies on sender reputation (IP, domain) when filtering emails. Poor reputation leads to deliverability issues.
  • Authentication: Proper email authentication (SPF, DKIM, DMARC) is crucial for verifying your identity and improving deliverability.
  • Complaint Rates: Microsoft is highly sensitive to spam complaint rates. High complaint rates can significantly damage your sender reputation.
  • Volume Sensitivity: Microsoft is sensitive to sudden changes in sending volume. Spikes in volume can trigger spam filters.
  • Engagement Metrics: User engagement (opens, clicks) plays a significant role. Low engagement can negatively impact deliverability.
  • List Hygiene: Poor list hygiene (outdated, invalid addresses) contributes to bounces and complaints, hurting reputation.
  • Shared IP Risks: Using a shared IP can be detrimental if other senders on the IP have poor sending practices.
  • Content Quality: Email content containing spam trigger words or poor formatting can increase the likelihood of being filtered as spam.

Key considerations

  • Monitor Reputation: Actively monitor your sender reputation using tools like Microsoft SNDS to identify and address potential issues.
  • Implement Authentication: Ensure you have properly configured SPF, DKIM, and DMARC records for your sending domains.
  • Clean Your Lists: Regularly clean your email lists to remove invalid, inactive, and unengaged subscribers.
  • Improve Content: Optimize your email content to avoid spam trigger words and ensure proper formatting.
  • Gradual Warm-up: If using a new IP address, gradually warm it up by increasing sending volume over time.
  • Consistent Volume: Maintain a consistent sending volume to avoid triggering spam filters.
  • Encourage Engagement: Encourage opens/clicks and get your users to move you from the junk folder or add to safe senders list.
  • A/B Testing: Perform A/B testing to improve deliverability, by discovering what your user base likes and optimise subject lines and email content.
Marketer view

Marketer from Email Geeks shares that Microsoft has been more problematic than usual, starting around October 2019. Their support usually cites unusual activity or SmartScreen filter recommendations.

January 2023 - Email Geeks
Marketer view

Marketer from Email Geeks mentions if an IP is blocked by Microsoft (visible in SNDS), stopping all traffic to Microsoft domains for 2-3 days, then restarting with small amounts of traffic to engaged recipients is usually effective.

October 2023 - Email Geeks
Marketer view

Email marketer from EmailToolTester shares that using a shared IP address can impact deliverability if other senders on the same IP are engaging in practices that harm the IP's reputation. Switching to a dedicated IP can give you more control over your reputation.

June 2022 - EmailToolTester
Marketer view

Email marketer from SendPulse shares that Microsoft prioritizes senders who properly authenticate their emails using SPF, DKIM, and DMARC. Implementing these authentication methods can improve deliverability by verifying your identity.

February 2024 - SendPulse
Marketer view

Marketer from Email Geeks explains that Microsoft is extremely sensitive to volume changes and a single spike can impact delivery for weeks.

June 2021 - Email Geeks
Marketer view

Email marketer from Mailjet explains that Microsoft is highly sensitive to complaint rates. If a significant percentage of recipients mark your emails as spam, your deliverability will suffer. Monitoring and managing your complaint rate is crucial.

April 2023 - Mailjet
Marketer view

Email marketer from Litmus explains that the content of your emails can impact deliverability. Using spam trigger words, excessive links, or poorly formatted HTML can increase the likelihood of your emails being filtered as spam.

June 2023 - Litmus
Marketer view

Email marketer from HubSpot explains that warming up your IP is important for deliverability. You need to gradually increase the volume of emails your sending from your IP over time to build a solid reputation.

June 2021 - HubSpot
Marketer view

Email marketer from Email Marketing Forum shares that inconsistent sending volumes can trigger spam filters. Sudden spikes in email volume, especially if you're normally sending low volume or have a new IP, can lead to Microsoft flagging your emails as spam.

February 2023 - Email Marketing Forum
Marketer view

Email marketer from Neil Patel Digital explains that your domain reputation is a critical factor. Microsoft heavily relies on sender reputation when filtering emails, so a poor reputation can significantly impact deliverability to Outlook and Hotmail addresses.

May 2024 - Neil Patel Digital
Marketer view

Email marketer from StackOverflow shares that user engagement is very important for deliverability. You need to try and encourage opens/clicks and get your users to move you from the junk folder or add to safe senders list.

October 2024 - StackOverflow
Marketer view

Marketer from Email Geeks says that if you can't produce steady volumes, you should stick to shared IPs because Microsoft has a high sensitivity to variations in volume.

April 2021 - Email Geeks
Marketer view

Email marketer from ActiveCampaign shares that doing A/B Testing to improve deliverability, is an effective way of discovering what your user base likes, and to optimise subject lines and email content.

September 2022 - ActiveCampaign
Marketer view

Email marketer from Reddit shares that poor list hygiene is a major cause of deliverability issues. Sending emails to outdated, invalid, or unengaged email addresses leads to bounces and spam complaints, which negatively impact your sender reputation.

September 2022 - Reddit

What the experts say
4Expert opinions

Poor email deliverability to Microsoft's Outlook and Hotmail platforms is influenced by several factors. One key element is sender reputation, which encompasses IP and domain standing, along with user engagement levels. Low engagement metrics on Hotmail, such as poor open and click-through rates coupled with high complaint rates, can negatively impact deliverability. Additionally, Outlook.com and Office365 should be treated differently concerning deliverability strategies. Furthermore, it is important to actively monitor blacklists and maintain high sender reputation.

Key opinions

  • Sender Reputation Focus: Microsoft heavily prioritizes sender reputation when determining email placement, including IP/Domain reputation and user engagement.
  • Engagement Metrics: Hotmail relies heavily on user engagement metrics (opens, clicks, complaints) for inbox placement decisions.
  • Differentiated Platforms: Outlook.com and Office365 do not behave identically in terms of deliverability and require distinct strategies.
  • Importance of Blocklists: Listings on major blocklists can severely impact deliverability to Microsoft platforms.

Key considerations

  • Monitor Sender Reputation: Continuously monitor your IP and domain reputation to identify and address any potential issues.
  • Improve Engagement: Implement strategies to increase user engagement (opens, clicks) and reduce complaint rates.
  • Address Platforms Individually: Develop distinct strategies tailored to the nuances of Outlook.com and Office365 for optimal deliverability.
  • Monitor Blocklists: Check regularly for blocklist listings, and take steps to be removed immediately.
Expert view

Expert from Word to the Wise explains that Microsoft places a heavy emphasis on sender reputation. This includes factors like IP address reputation, domain reputation, and user engagement. If these are low, your deliverability to Outlook/Hotmail will be impacted.

March 2024 - Word to the Wise
Expert view

Expert from Word to the Wise recommends actively monitoring blocklists, as a listing on a major blocklist can severely impact your deliverability to all email providers, including Microsoft. Regularly check your IP and domain against popular blocklists.

December 2022 - Word to the Wise
Expert view

Expert from Email Geeks says that Outlook.com and Office365 do not behave similarly with respect to deliverability.

August 2022 - Email Geeks
Expert view

Expert from Spam Resource explains that Hotmail heavily relies on user engagement metrics to determine inbox placement. Low open rates, click-through rates, and high complaint rates can signal to Hotmail that your emails are unwanted, leading to deliverability issues.

May 2021 - Spam Resource

What the documentation says
4Technical articles

Microsoft employs several mechanisms to protect its users from spam, impacting email deliverability. Throttling policies limit the volume of emails, especially from new IPs or domains. Monitoring IP reputation is crucial, and Microsoft provides the Sender Network Data Services (SNDS) tool for this. Implementing a Feedback Loop (FBL) allows senders to receive and act on spam complaints. Finally, a properly configured reverse DNS record (PTR) is essential for deliverability.

Key findings

  • Throttling: Microsoft implements strict throttling policies, which can negatively impact deliverability, especially for new IPs or domains sending large volumes.
  • SNDS Tool: Microsoft offers the Sender Network Data Services (SNDS) tool to monitor IP reputation, allowing senders to identify and address deliverability issues.
  • Feedback Loop (FBL): Implementing an FBL is vital for receiving spam complaints and removing subscribers marking emails as spam.
  • Reverse DNS (PTR) Record: A properly configured reverse DNS record (PTR) is essential for verifying the sender's identity and improving deliverability.

Key considerations

  • Monitor Throttling: Be aware of Microsoft's throttling policies, especially when starting a new campaign or using a new IP or domain.
  • Utilize SNDS: Regularly monitor your IP reputation using Microsoft's SNDS tool.
  • Implement FBL: Implement a Feedback Loop (FBL) to promptly address spam complaints.
  • Configure rDNS: Ensure your reverse DNS record (PTR) is correctly configured and matches your sending IP address to your domain name.
Technical article

Documentation from Microsoft Support explains that they implement strict throttling policies to protect their users from spam. Sending large volumes of email in a short period, especially from new IPs or domains, can trigger throttling and impact deliverability.

October 2021 - Microsoft Support
Technical article

Documentation from RFC explains that having a properly configured reverse DNS record (PTR record) that matches your sending IP address to your domain name is very important for deliverability. Ensure your rDNS record is properly setup.

February 2022 - RFC
Technical article

Documentation from Microsoft provides the Sender Network Data Services (SNDS) tool, which allows you to monitor your IP reputation and identify potential issues affecting deliverability to Microsoft domains. Regularly checking SNDS can help you proactively address problems.

July 2024 - Microsoft
Technical article

Documentation from Microsoft explains the importance of implementing a Feedback Loop (FBL) to receive reports of spam complaints from their users. This allows you to identify and remove subscribers who are marking your emails as spam.

June 2023 - Microsoft Support