Email deliverability varies significantly across mailbox providers because each operates with a unique and proprietary set of filtering technologies and algorithms. These systems assess various factors, including sender reputation, content, and user engagement, with differing weights and thresholds. Discrepancies also arise from a provider's specific user demographics, their individual risk tolerance for blocking mail, and how they interpret authentication standards. What is considered acceptable mail by one provider may be aggressively filtered by another, making consistent inbox placement a continuous challenge for senders.
11 marketer opinions
Email deliverability continues to differ among mailbox providers because each maintains distinct and often opaque anti-spam systems. These systems employ unique proprietary algorithms that evaluate incoming mail based on a varied blend of factors, including sender reputation, email content, and user engagement metrics. The specific weighting and strictness of these criteria, along with how each provider interprets and enforces authentication protocols, cause significant fluctuations in inbox placement for the same email campaigns across different providers.
Marketer view
Email marketer from Email Geeks shares an anecdote where an affiliate spammer used the argument that their competitors could send mail just fine and demanded equal treatment, which allowed the mailbox provider to apply equal treatment to all, implicitly highlighting the invalidity of such comparisons when dealing with bad actors.
29 Oct 2024 - Email Geeks
Marketer view
Email marketer from Email Geeks admits to having used the argument 'we are only having issue with 'your system' and nowhere else' in the past, but now understands much better how such discrepancies can happen, acknowledging it's still difficult to explain this to marketers.
12 Jun 2024 - Email Geeks
4 expert opinions
The varied approaches to email filtering among mailbox providers explain the persistent differences in deliverability, as each sets its own unique standards. These discrepancies arise from their distinct technical infrastructures, proprietary algorithms, and varying risk tolerance for blocking mail. Furthermore, the unique demographic makeup and preferences of each provider's user base significantly influence what mail is considered acceptable, leading to a complex landscape where successful delivery at one provider does not guarantee the same at another.
Expert view
Expert from Email Geeks explains that the argument 'but my mail to X is fine, tell Y that I'm not a bad sender' is a common point raised by senders, but mailbox providers have different standards, with some like Microsoft having a much higher threshold for 'good' mail and being happy to block mail that would be fine elsewhere. She also adds that higher volume domains like Google can statistically hide more 'ick' or problematic mail than smaller domains, as it's harder to 'lose in the noise' with fewer subscribers.
16 Mar 2022 - Email Geeks
Expert view
Expert from Email Geeks explains that Mailbox Providers (MBPs) have different demographics for customers, meaning what Gmail customers like vs. Comcast/Yahoo/GMX can be very different, making it entirely possible for the 'MBP X likes our mail but not MBP Y' scenario to occur.
17 Dec 2022 - Email Geeks
6 technical articles
Email deliverability varies among mailbox providers because each maintains its own unique, proprietary systems for evaluating incoming messages. Platforms like Google, Microsoft, and others develop distinct algorithms and filtering logic, which assess factors such as sender reputation, email content, and user engagement. The specific weighting and thresholds applied to these criteria differ significantly across providers, resulting in disparate inbox placement for the same email.
Technical article
Documentation from Google Postmaster Tools Help explains that Google, like other mailbox providers, utilizes its own proprietary reputation algorithms to assess sending domains and IPs. This means how an email is perceived and delivered to a Gmail inbox is based on Google's specific criteria, which differ from other providers' systems, leading to varied deliverability.
11 Oct 2024 - Google Postmaster Tools Help
Technical article
Documentation from Microsoft Docs explains that Microsoft's Exchange Online Protection (EOP) uses a distinct set of filtering technologies, including sender reputation, content analysis, and data from programs like Smart Network Data Services (SNDS). These unique, internal criteria mean that deliverability to Outlook.com or Microsoft 365 inboxes will differ from other providers who employ their own specific filtering logic and thresholds.
18 Jul 2022 - Microsoft Docs
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