Summary
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.
Key findings
- Recipient Interaction: Interaction with the sender's email affects deliverability.
- Spam Thresholds: Recipients have individual spam filtering thresholds.
- Feedback Loops: Recipient spam reports affect other recipients.
- Positive History: Past positive interactions improve deliverability.
- Quarantine: Emails can be trapped in individual quarantines.
- User-Based Filtering: Marking emails as unwanted affects others.
- Sender Reputation: Mimecast considers the sender's reputation.
- Internal Policies: Organizations have internal email filtering rules.
- Allow Lists: Recipients' allow lists bypass spam filters.
- Content Filtering: Email content triggers variable spam filters.
- Mimecast Rulesets: Differing Mimecast rulesets affect deliverability.
- Connection Limits: Mimecast imposes connection limits.
- Policy Inspection: Actions depend on policy; inspect logs.
Key considerations
- Encourage Engagement: Improve recipient interaction to boost delivery.
- Spam Threshold Awareness: Consider varied spam filtering settings.
- Avoid Spam Triggers: Minimize triggers for spam reports.
- Build Reputation: Maintain a positive sender reputation.
- Monitor Quarantine: Manage and monitor individual email quarantines.
- Policy Optimization: Understand and optimize policies for delivery.
- Check allow lists: Advise users to add the sender to their allow list if necessary.
- Connection Limits: Understand connection limits
What email marketers say
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.
Key opinions
- Sender Reputation: Mimecast's spam filtering depends on 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.
- Internal Policies: The recipient's organization may have internal email filtering rules/policies configured differently for user groups.
- Allow Lists: One recipient might have whitelisted the sender, bypassing spam filters for them, while another recipient has not.
- Content Filtering: Email content might trigger different spam filters for different recipients, based on words or phrases.
- Mimecast Rulesets: Recipients may have different Mimecast rulesets configured, leading to varying filtering outcomes.
- Policy Inspection: Actions depend on organizational policy. Inspecting Mimecast logs may reveal policy hits.
Key considerations
- Sender Reputation: Monitor and maintain a good sender reputation to avoid being flagged as spam.
- Internal Policies: Understand the recipient's organization's email filtering policies to optimize email content.
- Allow Lists: Encourage recipients to add the sender to their allow list if necessary.
- Content: Review email content to avoid triggering spam filters.
- Configuration Differences: Be aware that different recipients within the same organization may have differing Mimecast configurations.
- Log Analysis: Check Mimecast logs to understand why emails are being rejected and adjust email practices accordingly.
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
What the experts say
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.
Key opinions
- Recipient Interaction: Recipients actively interacting with the sender's emails are more likely to receive future emails, while those who don't may face deliverability issues.
- Personal Spam Thresholds: Recipients can set their own spam filtering thresholds, leading to differing outcomes for the same email.
- Recipient Feedback: If a recipient marks an email as spam, it can negatively impact future deliverability, even if the sender has a good reputation with others in the domain.
- Positive History: A history of positive interactions with other recipients in the same domain can improve deliverability.
- Email Quarantine: Emails can be trapped in an individual recipient's quarantine if they are not actively monitored or properly configured.
- User-Based Filtering: Mimecast may block emails to other recipients if one recipient marks the email as unwanted.
Key considerations
- Encourage Engagement: Encourage recipients to engage with your emails to improve deliverability.
- Spam Threshold Awareness: Be aware that recipients may have different spam threshold settings.
- Avoid Spam Triggers: Minimize actions that could lead to recipients marking your emails as spam.
- Build a Positive History: Focus on building a positive history of engagement within recipient domains.
- Quarantine Monitoring: Educate recipients on how to manage their email quarantine.
- Communicate the Issue: Inform recipients if they are blocking other recipients by labeling email as spam.
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
What the documentation says
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.
Key findings
- Sender Feedback Loops: Mimecast uses sender feedback loops. If one recipient marks an email as spam, Mimecast might block future emails from the same sender to other recipients.
- Personal Spam Thresholds: Mimecast allows individual users to set their own spam filtering thresholds. A stricter policy on one account can cause rejections where another accepts the mail.
- Blocked Sender Lists: If a recipient has blocked a sender, Mimecast will reject emails to that recipient, regardless of other recipients' settings.
- Connection Limits: Mimecast enforces connection limits from sending IPs. Exceeding these limits can cause delays or blocks for some users.
Key considerations
- Monitor Feedback Loops: Pay attention to feedback loops and address any issues that lead to spam reports.
- Inform Users: Advise users to be mindful of their spam filter settings and adjust as needed.
- Check Blocked Lists: Investigate if recipients have blocked your domain or IP address.
- Manage Connections: Ensure that you are not exceeding Mimecast's connection limits when sending emails.
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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