Summary
Sendgrid verification emails might be blocked by Mimecast while project invites are not due to a complex interplay of factors impacting sender reputation and email filtering. Key issues include different envelope froms, sender reputation problems, the content of verification emails triggering filters, DKIM and SPF misconfigurations, not explicitly permitting sending IP addresses and domains within Mimecast's policies, incorrect Auth0 email settings, volume/frequency anomalies, and poor list hygiene. Engaging with Mimecast support and A/B testing email content are essential troubleshooting steps.
Key findings
- Sender Reputation Issues: Newer or less warmed-up IPs, poor list hygiene, and high bounce rates associated with verification emails contribute to a lower sender reputation compared to project invites.
- Content and Filtering: Verification email content (keywords, links) may trigger Mimecast's spam filters or specific rules.
- Authentication Problems: DKIM, SPF, and DMARC may not be configured correctly for verification emails, but may be configured correctly for project invites.
- Mimecast Policies: Sending IPs and domains might not be explicitly permitted in Mimecast's sender policies, leading to unexpected blocks; invite emails may benefit from pre-existing rules.
- Volume/Frequency Anomalies: Lower volume/frequency can make the filtering more stringent.
- Auth0 Settings: Incorrect Auth0 configuration in relation to sendgrid, and setup of email settings can cause blocking issues.
- Feedback Loop Neglect: Failure to register and use the feedback loops provided by Mimecast to improve deliverability
Key considerations
- Contact Mimecast Support: Reach out to Mimecast support for insights into specific blocking reasons.
- Warm Up IPs: Implement IP warming strategies for new IPs.
- Improve List Hygiene: Use opt-in and remove stale addresses.
- Review and Optimize Content: Remove items causing the blocking.
- Set up DKIM/SPF/DMARC: Ensure that all authentication protocols are setup correctly.
- Monitor Domain Reputation: Monitor domain reputation.
- Update Mimecast Settings: Ensure sender IP/Domain are in Mimecast Policies
- Join Feedback Loops: Ensure sendgrid is registered for feedback loops with major ISPs including Mimecast.
- A/B Test: Try different email copy to isolate and fix issues with the copy.
What email marketers say
9 marketer opinions
Sendgrid verification emails can be blocked by Mimecast while project invites are not due to a variety of factors. These include differing sender reputations, content-based triggers, volume/frequency anomalies, IP warm-up status, authentication issues (SPF, DKIM, DMARC), and lack of monitoring of feedback loops. Engaging with Mimecast support and A/B testing email content are also recommended troubleshooting steps. Good list hygiene is critical to ensuring opt-in addresses and prevent triggering spam traps.
Key opinions
- Sender Reputation: Verification emails might be coming from a newer or less warmed-up IP address or domain than project invites, leading to lower reputation and increased scrutiny by Mimecast.
- Content Triggers: The specific content within verification emails (keywords, links, phrases) may trigger spam filters or specific rules within Mimecast, unlike project invites.
- Volume and Frequency: Lower volume and frequency of verification emails compared to project invites can raise suspicion and trigger anomaly detection systems.
- Authentication: Missing or incorrect SPF, DKIM, and DMARC records for verification emails can cause Mimecast to reject them, while project invites might be properly authenticated.
- Feedback Loops: Lack of registration and monitoring of Mimecast's feedback loops prevents identifying and addressing issues causing blocks.
- List Hygiene: Verification emails might be failing due to recipients not explicitly opting in or using outdated addresses, triggering Mimecast's spam traps.
Key considerations
- Contact Mimecast Support: Engage with Mimecast support for specific insights into the reasons for the blocks and guidance on resolution.
- Monitor Domain Reputation: Regularly monitor domain reputation using tools like Google Postmaster Tools and address any identified issues promptly.
- Dedicated IP Address: Consider using a dedicated IP address to build a distinct sender reputation, avoiding the negative impacts of shared IPs.
- A/B Test Content: A/B test different content and subject lines in verification emails to identify and eliminate elements triggering Mimecast's filters.
- Ensure all emails are properly authenticated.: Ensuring all emails are properly authenticated using SPF, DKIM and DMARC will help build trust with receiving mail servers such as Mimecast and improve deliverability.
- IP Warmup.: IP Warmup is critical for new sending IPs and domains. If project invites were sent from a warmed-up IP while verification emails are sent from a newer or less established IP, it can explain the discrepancy in deliverability.
Marketer view
Email marketer from Reddit shares that the volume and frequency of verification emails are usually lower than project invite emails. This difference in sending patterns could trigger anomaly detection systems within Mimecast. Invite emails may also be getting caught in filters due to being initiated by a real person, and a real action.
10 Jan 2023 - Reddit
Marketer view
Email marketer from SparkPost shares that the content of verification emails might inadvertently trigger spam filters or specific rules within Mimecast. For example, using phrases like 'verify your account' or including certain types of links could be problematic.
26 Mar 2025 - SparkPost
What the experts say
7 expert opinions
Experts suggest that Sendgrid verification emails being blocked by Mimecast, while project invites are not, is often due to a combination of factors. These include differing sender reputations stemming from poor list hygiene and high bounce rates, not properly warming up the IP address. It is also important to register for Mimecast’s feedback loop to identify and address recipient complaints. Additionally, some experts recommend contacting Mimecast support directly for assistance as the described blocking behavior may not make sense based on the outlined email setup.
Key opinions
- List Hygiene: Poor list hygiene, including sending to recipients who haven't explicitly opted in or using outdated addresses, can trigger Mimecast's spam traps.
- Bounce Rates: High bounce rates from verification emails negatively impact sender reputation, potentially leading to Mimecast blocking these emails.
- Feedback Loops: Failing to register for and monitor Mimecast's feedback loop prevents senders from identifying and addressing recipient complaints.
- IP Warmup: The verification emails are being sent from a new/less warmed up IP than the project invites.
Key considerations
- Contact Mimecast Support: Reach out to Mimecast support for specific insights into the blocking behavior, as it might not align with the expected email setup.
- Improve List Hygiene: Implement strategies to improve list hygiene, such as double opt-in and regular list cleaning.
- Monitor Bounce Rates: Actively monitor bounce rates and address the underlying causes to prevent negative impacts on sender reputation.
- Register for Feedback Loop: Register for Mimecast's feedback loop to receive reports on spam complaints and proactively remove problematic recipients.
- IP Warmup: Warm up the verification email IPs properly.
Expert view
Expert from Word to the Wise says IP Warmup is critical for new sending IPs and domains. If project invites were sent from a warmed-up IP while verification emails are sent from a newer or less established IP, it can explain the discrepancy in deliverability.
21 Jun 2022 - Word to the Wise
Expert view
Expert from Email Geeks states it's exceedingly unlikely that the envelope from is the same using two different ESPs, suggesting it's almost impossible.
12 Jul 2024 - Email Geeks
What the documentation says
5 technical articles
Documentation indicates that Sendgrid verification emails being blocked by Mimecast while project invites are not can stem from various configuration and policy issues. These include sender reputation problems, content-based triggers, DKIM and SPF misconfigurations, not explicitly permitting sending IP addresses and domains within Mimecast's policies, and incorrect Auth0 email settings.
Key findings
- Sender Reputation: Poor sender reputation can lead to email blocks, as Mimecast may filter emails from senders with a history of sending spam or unwanted mail.
- Content Filters: The content of verification emails, including specific keywords or attachments, might trigger Mimecast's content filters.
- DKIM Configuration: Incorrect DKIM configuration for sending domains/subdomains can make Mimecast suspicious of unauthenticated verification emails.
- SPF Records: Incorrect or missing SPF records can cause Mimecast to reject emails, as they fail to authorize Sendgrid to send emails on behalf of your domain.
- Mimecast Sender Policies: Sending IP addresses and domains might not be explicitly permitted in Mimecast's sender policies, leading to unexpected blocks.
- Auth0 Settings: Incorrect Auth0 email settings that do not align with SendGrid's requirements can contribute to deliverability issues.
Key considerations
- Review Sender Reputation: Assess and improve sender reputation by ensuring good email practices, such as permission-based sending and proper list hygiene.
- Optimize Email Content: Review and optimize the content of verification emails to avoid triggering spam filters or specific rules within Mimecast.
- Verify DKIM Configuration: Ensure that DKIM is properly configured for all sending domains and subdomains.
- Configure SPF Records: Correctly configure SPF records to authorize Sendgrid to send emails on behalf of your domain.
- Update Mimecast Sender Policies: Ensure that sending IP addresses and domains are explicitly permitted in Mimecast's sender policies.
- Align Auth0 Settings: Verify that Auth0 email settings are correctly configured to align with SendGrid's requirements.
Technical article
Documentation from SendGrid Support explains that if DKIM is not properly configured for both sending domains/subdomains (project invites vs. verification emails), Mimecast could be more suspicious of the unauthenticated verification emails, leading to blocks.
29 Dec 2024 - SendGrid
Technical article
Documentation from Mimecast shares that ensuring your sending IP addresses and domains are explicitly permitted in Mimecast's sender policies can prevent unexpected blocks. The invite emails may be benefitting from pre-existing rules.
9 Mar 2024 - Mimecast
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