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Summary

Emails landing in the junk folder, particularly with Hotmail and other Microsoft email services (Outlook, Live), are a common and frustrating deliverability issue for senders. Even with proper email authentication and seemingly good sending practices, messages can still be misclassified as spam. This often stems from Microsoft's unique filtering algorithms, which place a strong emphasis on recipient engagement and the sender's established reputation. New domains and shared IP addresses can be particularly susceptible to these filtering challenges, as they lack a history of positive interactions.

Key findings

What email marketers say

Email marketers often find Microsoft's filtering to be a particular challenge compared to other mailbox providers. Many recount experiences where emails that land perfectly in Gmail or other inboxes are consistently junked by Hotmail or Outlook. The consensus points towards Microsoft's unique and often opaque methods for assessing sender reputation, heavily leaning on recipient behavior and historical data. This leads to a strong emphasis on list hygiene, explicit subscriber consent, and managing recipient expectations.

Key opinions

Marketer view

Marketer from Email Geeks explains their current issue with Hotmail, stating all emails are going to junk. They report starting a new list last week with 500 sign-ups and sending 3 fitness-related emails per week. Despite this, their bounce rate is low at 0.3% with only 5 unsubscribes, and Hotmail constitutes 30% of their list. They mention having contacted their ESP, Drip, but have not yet received a response. Initial checks revealed that not all emails were going to Hotmail junk, but spam testing indicated failures for Hotmail and mail.com, despite a SpamAssassin score of -0.3. This highlights the varying filtering logic across different providers.

10 May 2020 - Email Geeks

Marketer view

Marketer from Email Geeks reports that they are in full control of their sign-up sources, confirming they are not purchasing lists or engaging in questionable acquisition methods. They also assert that their emails are well-crafted and deliver relevant information to contacts. This indicates strong internal practices regarding content and list quality. Furthermore, all necessary information, including email frequency (3 contacts per week) and content (fitness workouts), is clearly stated on their sign-up page. This transparent approach should, in theory, lead to better subscriber engagement and fewer complaints, yet they still face Hotmail junking issues.

10 May 2020 - Email Geeks

What the experts say

Deliverability experts consistently highlight that Microsoft's (Hotmail, Outlook) email filtering is distinct and highly sensitive to sender reputation, particularly emphasizing recipient engagement. They caution that traditional spam scores are often irrelevant and that new sending IPs or domains face significant hurdles during the warmup period. Expert advice centers on understanding Microsoft's specific criteria, proactively managing subscriber behavior, and ensuring all technical aspects, especially rDNS for dedicated IPs, are impeccably configured.

Key opinions

Expert view

Expert from Email Geeks explains that testing emails against SpamAssassin is largely irrelevant for Microsoft and other major mailbox providers. This is because these providers, including Microsoft, do not use SpamAssassin as part of their filtering logic. Instead, they employ more sophisticated, proprietary systems that heavily factor in recipient engagement and sender reputation, rendering a good SpamAssassin score meaningless for inbox placement with these large providers.

10 May 2020 - Email Geeks

Expert view

Expert from Email Geeks states that most large mailbox providers, including Microsoft, measure how their recipients interact with messages as a key indicator of whether those messages are wanted or unwanted. This crucial metric is referred to as 'engagement.' Therefore, if enough people see emails in their inbox but ignore, delete, or mark them as junk, it will negatively impact future deliverability. Conversely, positive actions like opening, reading, and replying will have a positive effect on where future emails land.

10 May 2020 - Email Geeks

What the documentation says

Official documentation from email service providers and mailbox operators often outlines best practices for senders to ensure high deliverability. These documents consistently emphasize adherence to industry standards like email authentication, maintaining a good sender reputation, and ensuring compliance with anti-spam regulations. For Microsoft, specifically, while detailed internal filtering logic isn't fully public, their guidelines often hint at the importance of user interaction and a clean sending history. They provide tools and guidance for senders to self-diagnose and improve their standing.

Key findings

Technical article

Documentation from Microsoft's Outlook.com Postmaster Tools states that senders can use their services to gain insight into their email sending reputation to Outlook.com users. These tools provide data on complaint rates, spam trap hits, and other metrics that are crucial indicators of sender health. They emphasize that maintaining a low complaint rate and a positive sender reputation is key to achieving consistent inbox placement, underscoring the importance of monitoring these specific metrics.

20 Feb 2023 - Outlook.com Postmaster Tools

Technical article

Documentation from Microsoft's sender support pages recommends that senders implement SPF, DKIM, and DMARC records for their sending domains. These authentication methods are presented as essential steps to verify sender identity and prevent email spoofing and phishing attempts. While not a silver bullet for inbox placement, they are fundamental requirements that help establish a baseline of trust with Microsoft's mail servers, without which emails are highly likely to be rejected or junked.

15 Mar 2023 - Microsoft Sender Support

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