Welcome to our expert guide on Mimecast email delivery warnings. As a seasoned expert in email security and delivery, I'm thrilled to take you on a journey through the intricate world of Mimecast email management. In this article, we'll explore the common causes of email delivery warnings, delve into troubleshooting techniques, and provide valuable tips to ensure your emails reach their intended recipients without any interruptions. Let's dive in!

Understanding Mimecast Email Delivery Warnings

Mimecast is a leading provider of email security and management solutions, offering a range of services to protect organizations from email threats, such as spam, malware, and phishing attempts. While Mimecast is highly effective in safeguarding your email communication, you might encounter email delivery warnings under specific circumstances. Here are some common scenarios that trigger Mimecast email delivery warnings:

1. Large Email Attachments

When an email contains large attachments, Mimecast may apply additional scrutiny to ensure efficient delivery. Large attachments can slow down email delivery and may trigger temporary delivery delays.

2. Suspicious Email Content

If an email's content exhibits characteristics commonly found in spam or phishing attempts, Mimecast's advanced security algorithms might flag it as potentially malicious. While this is a vital feature to protect users, legitimate emails with certain keywords or attachments may inadvertently trigger a warning.

3. Email Reputation and Authentication

Mimecast heavily relies on sender reputation and email authentication methods like SPF, DKIM, and DMARC to verify the legitimacy of emails. If your domain or email server lacks proper authentication, Mimecast may issue a warning to safeguard its recipients.

Troubleshooting Mimecast Email Delivery Warnings

Receiving a Mimecast email delivery warning doesn't necessarily indicate a problem with your email delivery. However, it's essential to address these warnings promptly to ensure smooth email communication. Here are some troubleshooting steps:

1. Check Email Content

Review the content of your email for any suspicious elements or spam-like characteristics. Avoid using spammy keywords, excessive exclamation marks, or misleading subject lines.

2. Optimize Attachments

If your email contains large attachments, consider using file-sharing services or cloud storage links to reduce the attachment size and improve deliverability.

3. Authenticate Your Emails

Properly authenticate your email domain with SPF, DKIM, and DMARC records to establish a trustworthy sender reputation.

4. Review Mimecast Policies

Understand Mimecast's email security policies and adjust your email content and attachments accordingly to comply with their guidelines.

Expert Tips for Seamless Mimecast Email Delivery

As an expert in email security and delivery, I have compiled some valuable tips to ensure seamless email delivery with Mimecast:

1. Regularly Monitor Mimecast Alerts

Stay vigilant and regularly monitor Mimecast alerts to detect any potential issues or delivery warnings. Being proactive allows you to address them promptly and maintain smooth email delivery.

2. Implement Email Authentication

Authenticate your email domain using SPF, DKIM, and DMARC to establish trust with email service providers and ensure consistent email delivery.

3. Engage in Email List Management

Maintain a clean and engaged email list by regularly removing invalid or inactive email addresses. Engage with your subscribers to keep them interested in your content and reduce the likelihood of triggering warnings.

4. Educate Your Team

Educate your team about email security best practices, including avoiding spam-like content and suspicious attachments. A well-informed team contributes to a secure and effective email communication.


Mimecast is a powerful tool to protect your organization from email threats. Understanding email delivery warnings and taking proactive steps to address them ensures smooth email communication and enhances your email security posture. By following the expert tips provided in this article, you can optimize your email management with Mimecast and deliver messages with confidence.

Remember, staying vigilant and informed is key to successful email delivery. Elevate your email security game with Mimecast and enjoy the benefits of efficient and secure email communication.