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Microsoft Defender for Office 365 vs Mimecast Email Security comparison

 

Comparison Buyer's Guide

Executive SummaryUpdated on Apr 20, 2025

Review summaries and opinions

We asked business professionals to review the solutions they use. Here are some excerpts of what they said:
 

ROI

Sentiment score
7.4
Organizations saw increased productivity, cost savings, and enhanced security with Microsoft Defender for Office 365's advanced features.
Sentiment score
3.5
Mimecast Email Security prevents breaches and blocks phishing, significantly enhancing business security despite challenges in quantifying its ROI.
It has also decreased our time to detection and response by about 15 to 20 percent.
There is definitely a return on investment when using Mimecast, as it blocks phishing emails, reducing the risk of significant financial losses.
 

Customer Service

Sentiment score
6.9
Microsoft Defender for Office 365 support is praised for responsiveness but has inconsistencies, especially in first-level assistance.
Sentiment score
5.5
Mimecast Email Security support is responsive but often redirects to unclear articles; mixed reviews on speed and flexibility.
Any issues are addressed quickly by Microsoft's support.
Customer service and support have been fantastic.
Support personnel are hesitant to engage in remote sessions, preferring to share documentation via email.
Mimecast technical support is generally quite good.
 

Scalability Issues

Sentiment score
8.1
Microsoft Defender for Office 365 scales effectively, seamlessly expanding capacity with minimal maintenance, suitable for large and growing organizations.
Sentiment score
7.9
Mimecast Email Security is scalable, adaptable, and allows easy license adjustments but may face occasional feature challenges.
We have never faced scalability problems, and Microsoft manages it effectively.
 

Stability Issues

Sentiment score
7.7
Microsoft Defender for Office 365 is reliable, with 99.9% availability and efficient bug fixes, offering seamless performance and stability.
Sentiment score
7.5
Mimecast Email Security is praised for stability and integration, with rare downtimes, few bugs, and high user satisfaction.
The solution is stable, as we have been using it for the past two years.
 

Room For Improvement

Microsoft Defender for Office 365 needs enhanced threat detection, integration, support, usability, documentation, and transparent pricing to address customer concerns.
Mimecast Email Security struggles with detection, user interface, support, costs, configurations, and database reliance, affecting overall user satisfaction.
The main area for improvement is simplifying the implementation and rollout process.
Microsoft could improve by offering recommendations for domain spoofing attacks, especially scenarios where DNS records like SPF, DKIM, and DMARC are not properly published.
I would reduce the cost.
A lot of emails were missed despite being known samples.
 

Setup Cost

Microsoft Defender for Office 365, often pricey for SMEs, offers extensive security features with complex user-based licensing.
Mimecast Email Security is seen as costly, though features and updates justify the price; competitors offer cheaper alternatives.
Microsoft is quite affordable with a lot of features available for any size organization.
Money-wise, it is a part of the Office 365 suite, making it slightly more expensive compared to Trend Micro.
The pricing is higher for Mimecast, particularly for the Indian market, where it is considered expensive.
 

Valuable Features

Microsoft Defender for Office 365 offers integrated protection with features like anti-malware and threat detection, enhancing security through AI.
Mimecast Email Security excels in threat protection, spam filtering, and user-friendliness, with strong Microsoft 365 integration and technical support.
It ranks the threats and allows us to prioritize those hitting us the hardest, such as email threats.
It provides end-to-end visibility on email threats such as phishing, extending beyond Exchange Online Protection.
Microsoft Defender for Office 365 is now part of a centralized tenant for my entire group.
A distinct advantage of Mimecast is its ability to block phishing and impostor attacks, which are significant threats currently.
One of the most useful features is the threat remediation module, which can be used to remove malicious emails that may have been delivered or manually remove them.
 

Categories and Ranking

Microsoft Defender for Offi...
Average Rating
8.4
Reviews Sentiment
7.1
Number of Reviews
49
Ranking in other categories
Email Security (1st), Advanced Threat Protection (ATP) (1st), Microsoft Security Suite (11th)
Mimecast Email Security
Average Rating
8.0
Reviews Sentiment
5.9
Number of Reviews
30
Ranking in other categories
Office 365 Protection (5th), Secure Email Gateway (SEG) (3rd)
 

Mindshare comparison

As of May 2025, in the Secure Email Gateway (SEG) category, the mindshare of Microsoft Defender for Office 365 is 29.5%, down from 39.3% compared to the previous year. The mindshare of Mimecast Email Security is 11.2%, down from 16.1% compared to the previous year. It is calculated based on PeerSpot user engagement data.
Secure Email Gateway (SEG)
 

Featured Reviews

Tolu Omolaja - PeerSpot reviewer
Great URL scanning and attachment scanning, but I would like more proactive threat analysis
The two main features that prove most beneficial for us are URL scanning and attachment scanning. URL scanning involves an automatic scan of links and emails. When a user clicks on a link within an email, the system promptly checks the link's safety. If the link is deemed safe, access is granted automatically. However, if it is flagged as unsafe, we receive feedback and notification to caution us about the potentially harmful link. At this point, we are presented with the option to proceed or return. I have personally witnessed the system identify a few unsafe links, making this the primary advantage of using the solution. The second crucial aspect is the scanning of attachments. When an email containing an attachment arrives, we receive a notification of the new email, along with information that the attachment is being scanned for threats. This additional layer of security provides peace of mind for our organization. While Microsoft Defender for Office 365 offers numerous features, these two stand out as particularly impressive and valuable to us.
Frank Rawson - PeerSpot reviewer
It gives clients peace of mind and helps them educate their users about threats
A few years ago, our team found the implementation to be somewhat challenging. It has gotten easier as we've grown more experienced. The difficulty depends on the expertise of the person doing it. I don't work with Mimecast every day, so it might be more difficult for me than it is for one of my techs who regularly does Mimecast implementations. It requires some specific in-depth product knowledge and an understanding of email solutions. The deployment time varies. In South Africa, it depends on who you use to deploy it. If you use one of Mimecast's local partners, it can take up to two weeks because of their process. However, it's only about four to eight hours of work. After deployment, there isn't much maintenance aside from supporting and educating your customers. Users require constant education on how to use the Mimecast client and release an email that has been blocked.
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Answers from the Community

HM
May 4, 2023
May 4, 2023
In my opinion, all gateways including Mimecast or Defender for O365 or ProofPoint work hand-in-hand in their respective mechanics and algorithms built. And definitely has its own advantages. However, I have been using it for my customers' MDO which is far better. I would say relying on gateways is important but at the same time USER education and reporting back to the IT administrator far impor...
See 2 answers
TL
Apr 25, 2023
Greetings Matingou, Defender for O365 I would say would suffice as it has all the tools included in Mimecast in just one single tool, may take some time to navigate at first as it gives a lot of information in just one tool but once you know your way around, you will be able to have good visibility on your email threats landscape by provides a range of protections against email-based threats such as spam, phishing, malware, and etc. It also includes features such as URL protection and attachment scanning to prevent users from clicking on malicious links or downloading harmful files. but on the other hand, Mimecast might be needed, if you require compliance measures, including data loss prevention, archiving, and encryption. It also provides greater visibility and control over email security, allowing you to monitor and manage threats in real-time. Hope this helps.
BK
May 4, 2023
In my opinion, all gateways including Mimecast or Defender for O365 or ProofPoint work hand-in-hand in their respective mechanics and algorithms built. And definitely has its own advantages. However, I have been using it for my customers' MDO which is far better. I would say relying on gateways is important but at the same time USER education and reporting back to the IT administrator far important as well. 
 

Top Industries

By visitors reading reviews
Computer Software Company
16%
Financial Services Firm
9%
Manufacturing Company
8%
Government
6%
Computer Software Company
15%
Financial Services Firm
8%
Manufacturing Company
7%
Construction Company
5%
 

Company Size

By reviewers
Large Enterprise
Midsize Enterprise
Small Business
 

Questions from the Community

What do you like most about Microsoft Defender for Office 365?
Threat Explorer is an invaluable tool for me, and it plays a crucial role in helping me discern the origins of various email campaigns, pinpointing where they emanate from, and identifying the indi...
What is your experience regarding pricing and costs for Microsoft Defender for Office 365?
Money-wise, it is a part of the Office 365 ( /products/office-365-reviews ) suite, making it slightly more expensive compared to Trend Micro. Although Defender is free, you have to pay separately f...
What needs improvement with Microsoft Defender for Office 365?
The main area for improvement is simplifying the implementation and rollout process. There are many conditions to be met, making it challenging to ensure every system is protected. Troubleshooting ...
What do you like most about Mimecast Email Security with Targeted Threat Protection?
The interface of this solution is very easy to navigate and user-friendly. There is no delivery in email and other communications, making it reliable. The configuration is relatively easy.
What is your experience regarding pricing and costs for Mimecast Email Security with Targeted Threat Protection?
The pricing is higher for Mimecast, particularly for the Indian market, where it is considered expensive.
What needs improvement with Mimecast Email Security with Targeted Threat Protection?
There is nothing that notably stands out in need of improvement at present.
 

Also Known As

MS Defender for Office 365
Mimecast Email Security with Targeted Threat Protection
 

Overview

 

Sample Customers

Microsoft Defender for Office 365 is trusted by companies such as Ithaca College.
Azizi Developments, Affinity Credit Union, Aftercare, Al Abbar Group
Find out what your peers are saying about Microsoft Defender for Office 365 vs. Mimecast Email Security and other solutions. Updated: April 2025.
849,686 professionals have used our research since 2012.