Email deliverability discrepancies with Mimecast arise from a confluence of factors related to sender reputation, recipient behavior, and Mimecast's filtering mechanisms. These include: different levels of recipient interaction with the sender; individual spam threshold settings; recipient feedback loops where marking emails as spam impacts other recipients; the sender's history of positive interactions within the domain; quarantine settings; user-based filtering; internal organizational policies; sender allow lists; content-based filtering variations; differing Mimecast rulesets; connection limits; and specific policy hits. Ultimately, actions depend on the recipient or organizational policies.
6 marketer opinions
Emails may be delivered to one recipient but rejected for another by Mimecast due to several factors. These include the sender's reputation, differing internal email filtering rules within the recipient's organization, individual recipients' allow lists, content-based spam filtering variations, differing Mimecast rulesets between recipients, and organization policy configurations. Inspecting Mimecast logs can provide insight into specific policy hits.
Marketer view
Email marketer from Reddit explains that the organization receiving the email might have internal email filtering rules or policies. They may be configured differently for different groups of users.
18 Dec 2021 - Reddit
Marketer view
Email marketer from EmailGeek explains that Mimecast considers the sender's reputation. A sender with a low reputation score may have emails rejected for some recipients but not others, depending on how aggressively each recipient's organization filters based on reputation.
20 Apr 2023 - EmailGeek
7 expert opinions
Email delivery discrepancies within Mimecast can stem from varying levels of engagement between recipients and the sender, personalized spam thresholds, recipient feedback loops (marking emails as spam), the sender's history of positive interactions with other recipients within the same domain, and emails being trapped in individual recipient's quarantine. User-based filtering, where one recipient marking an email as unwanted impacts delivery to others, also plays a role.
Expert view
Expert from Word to the Wise explains that if one recipient marks an email as spam or unwanted, Mimecast may use this information to block similar emails from reaching other recipients within the same organization. This is a form of user-based filtering.
17 May 2023 - Word to the Wise
Expert view
Expert from Email Geeks explains that if Y marks the email as spam, it will go to the spam folder, even if the sender has a history with others at the domain
13 Nov 2023 - Email Geeks
4 technical articles
Mimecast's behavior of delivering email to one recipient but rejecting it for another is influenced by several factors detailed in its documentation. Sender feedback loops, where spam reports from one user impact deliverability to others, personalized spam filtering thresholds set by individual users, explicit blocking of senders by recipients, and connection limits from single sending IPs all contribute to these discrepancies.
Technical article
Documentation from Mimecast explains that Mimecast uses sender feedback loops. If a recipient marks an email as spam, Mimecast can use this information to block future emails from the same sender to other recipients within the organization.
2 May 2024 - Mimecast
Technical article
Documentation from Mimecast explains that Mimecast allows individual users to set their own spam filtering thresholds. One recipient may have a stricter spam policy than another, leading to different outcomes for the same email.
9 Mar 2025 - Mimecast
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