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Microsoft Defender for Office 365 vs Mimecast Email Security comparison

 

Comparison Buyer's Guide

Executive SummaryUpdated on Nov 2, 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
6.9
Microsoft Defender for Office 365 offers strong ROI through security enhancements, cost savings, and improved company productivity despite measurement challenges.
Sentiment score
5.5
Users have mixed ROI views on Mimecast Email Security, noting its effectiveness against threats but questioning cost-efficiency.
It has also decreased our time to detection and response by about 15 to 20 percent.
Technology support manager at Alfred State College
Overall, cost of owning and operating our system goes down.
Designation Chief Consultant at Avtow
It's hard to quantify the return on investment we've seen from Microsoft Defender for Office 365.
Chief Architect at a tech vendor with 1,001-5,000 employees
There is definitely a return on investment when using Mimecast, as it blocks phishing emails, reducing the risk of significant financial losses.
Senior Tech. Lead at WE
 

Customer Service

Sentiment score
5.8
Microsoft Defender for Office 365 users rate support highly, praising its responsiveness and 24/7 availability, despite occasional documentation and communication issues.
Sentiment score
5.6
Mimecast Email Security support is helpful but has mixed reviews due to delays and reliance on indirect solutions.
Over the past two years, there have been no critical problems.
Solution Consultant at BIM Group of Companies
we opened tickets, and they typically resolve them quickly.
Chief Architect at a tech vendor with 1,001-5,000 employees
With a subscription for Microsoft Defender for Office 365, it is an eight. Without it, it is a six.
Manager at a tech services company with 10,001+ employees
Support personnel are hesitant to engage in remote sessions, preferring to share documentation via email.
Senior Tech. Lead at WE
Mimecast technical support is generally quite good.
Information Security Analyst at Enfield Central Library
I would rate my experience with technical support of Mimecast Email Security between seven and eight out of ten for their support.
Email Security Engineer at Logic Infosecurity
 

Scalability Issues

Sentiment score
7.8
Microsoft Defender for Office 365 offers scalable, efficient protection for large enterprises, ensuring seamless growth across diverse industries.
Sentiment score
7.0
Mimecast Email Security is praised for adaptability and scalability, supporting various industries despite minor feature challenges.
We have never faced scalability problems, and Microsoft manages it effectively.
Solution Consultant at BIM Group of Companies
Microsoft Defender for Office 365 scales transparently for us, as we grew from 1,000 users to 3,000 users, and we didn't notice much difference.
Chief Architect at a tech vendor with 1,001-5,000 employees
Microsoft Defender for Office 365 scales with the growing needs of my company well.
Senior Client Director and Advisory Service Leader at Crossfuze
If Mimecast Email Security introduces API solutions, it will dominate the market.
Email Security Engineer at Logic Infosecurity
 

Stability Issues

Sentiment score
7.7
Microsoft Defender for Office 365 provides 99.9% uptime with minor issues, ensuring reliable performance and seamless cloud integration.
Sentiment score
7.5
Mimecast Email Security is reliable and stable, with minimal glitches, occasional delays, and high user ratings for performance.
I would rate the stability of Microsoft Defender for Office 365 as 10 over 10 because it's highly available, it works, and it does the job it is meant to do.
Cloud Solutions Architect at a tech services company with 201-500 employees
I have not experienced any downtime, crashes, or performance issues because of Defender.
Technology Associate at a financial services firm with 51-200 employees
The solution is stable, as we have been using it for the past two years.
Solution Consultant at BIM Group of Companies
They confirm it's a good solution where only one or two rare emails get through, while the rest are properly blocked without any issues.
Email Security Engineer at Logic Infosecurity
 

Room For Improvement

Users call for enhanced virus detection, cross-platform support, and pricing transparency in Microsoft Defender for Office 365.
Mimecast Email Security needs improvements in pricing, detection, complexity, user interface, support, and reducing false positives and attachment issues.
The main area for improvement is simplifying the implementation and rollout process.
Infrastructure and Security Lead at Vedanta
Microsoft could improve by offering recommendations for domain spoofing attacks, especially scenarios where DNS records like SPF, DKIM, and DMARC are not properly published.
Solution Consultant at BIM Group of Companies
There is a different console for different things; I just want one consolidated console.
Senior Director, Security Architecture & Engineering at a leisure / travel company with 10,001+ employees
A lot of emails were missed despite being known samples.
Senior Tech. Lead at WE
Mimecast Email Security is somewhat expensive compared to the competition in the Indian market.
Co-Founder & VP-Sales at QuantumShield Technologies LLP
We discussed the phishing aspect, the DNS system, and the key rotation.
Senior Security Engineer at ManpowerGroup
 

Setup Cost

Microsoft Defender for Office 365 pricing is seen as flexible but potentially expensive, offering value in comprehensive security features.
Mimecast Email Security is often seen as costly due to user-based licensing and added fees, despite potential discounts.
We've likely saved 30% of costs.
Designation Chief Consultant at Avtow
Money-wise, it is a part of the Office 365 suite, making it slightly more expensive compared to Trend Micro.
Infrastructure and Security Lead at Vedanta
Microsoft is quite affordable with a lot of features available for any size organization.
Solution Consultant at BIM Group of Companies
The pricing is higher for Mimecast, particularly for the Indian market, where it is considered expensive.
Senior Tech. Lead at WE
 

Valuable Features

Microsoft Defender for Office 365 enhances email security with anti-phishing, anti-malware, threat intelligence, and seamless integration for efficient management.
Mimecast Email Security offers strong threat protection, easy setup, seamless Microsoft 365 integration, and excellent scalability and support.
It ranks the threats and allows us to prioritize those hitting us the hardest, such as email threats.
Technology support manager at Alfred State College
It provides end-to-end visibility on email threats such as phishing, extending beyond Exchange Online Protection.
Solution Consultant at BIM Group of Companies
The value of the DLP feature is significant to us because we have internal data, sometimes sensitive, and the users may not always be aware of security and privacy, which might lead them to send out information mistakenly to external parties.
Chief Architect at a tech vendor with 1,001-5,000 employees
A distinct advantage of Mimecast is its ability to block phishing and impostor attacks, which are significant threats currently.
Senior Tech. Lead at WE
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.
Information Security Analyst at Enfield Central Library
Mimecast Email Security includes the best gateway solution across all Cisco, Trend Micro, and other solutions.
Email Security Engineer at Logic Infosecurity
 

Categories and Ranking

Microsoft Defender for Offi...
Ranking in Secure Email Gateway (SEG)
1st
Average Rating
8.4
Reviews Sentiment
6.8
Number of Reviews
60
Ranking in other categories
Email Archiving (1st), Email Security (1st), Advanced Threat Protection (ATP) (2nd), Microsoft Security Suite (10th)
Mimecast Email Security
Ranking in Secure Email Gateway (SEG)
4th
Average Rating
8.0
Reviews Sentiment
5.9
Number of Reviews
32
Ranking in other categories
Office 365 Protection (3rd)
 

Mindshare comparison

As of January 2026, in the Secure Email Gateway (SEG) category, the mindshare of Microsoft Defender for Office 365 is 24.2%, down from 31.1% compared to the previous year. The mindshare of Mimecast Email Security is 14.4%, up from 12.5% compared to the previous year. It is calculated based on PeerSpot user engagement data.
Secure Email Gateway (SEG) Market Share Distribution
ProductMarket Share (%)
Microsoft Defender for Office 36524.2%
Mimecast Email Security14.4%
Other61.4%
Secure Email Gateway (SEG)
 

Featured Reviews

Emeka Ndulu - PeerSpot reviewer
Cloud Solutions Architect at a tech services company with 201-500 employees
Improves threat visibility and response while reducing manual tasks and training users against phishing
I appreciate the attack simulation feature whereby I get to train users and educate them on how to identify phishing emails and spam emails, as well as the anti-spam protection. It gives me visibility into my threat environment and threat landscape to ensure that I am one step ahead of any likelihood of threats within my environment. I get to detect it and respond, so the threat intelligence is very effective. Microsoft security solutions save my time. It saves money because once I protect my environment, I don't lose money. It has decreased my detection time and my time to respond.
RP
Senior Tech. Lead at WE
Block significant threats with enhanced phishing prevention
In terms of efficacy, Proofpoint is better than Mimecast, though it's a little difficult to manage. A distinct advantage of Mimecast is its ability to block phishing and impostor attacks, which are significant threats currently. Security is a major feature where email security tools like Mimecast have delivered value by identifying and preventing phishing emails.
report
Use our free recommendation engine to learn which Secure Email Gateway (SEG) solutions are best for your needs.
879,371 professionals have used our research since 2012.
 

Answers from the Community

HM
Senior System Engineer at AfDB
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
Senior IT Security Specialist at a tech services company with 1,001-5,000 employees
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
IT Manager at vTech4U
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
15%
Financial Services Firm
8%
Manufacturing Company
8%
Comms Service Provider
6%
Computer Software Company
14%
Financial Services Firm
8%
Manufacturing Company
7%
Comms Service Provider
5%
 

Company Size

By reviewers
Large Enterprise
Midsize Enterprise
Small Business
By reviewers
Company SizeCount
Small Business23
Midsize Enterprise10
Large Enterprise31
By reviewers
Company SizeCount
Small Business17
Midsize Enterprise7
Large Enterprise11
 

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 needs improvement with Microsoft Defender for Office 365?
The inbuilt analysis of false positives can be faster. It's not slow, but it can be faster.
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 needs improvement with Mimecast Email Security with Targeted Threat Protection?
Mimecast Email Security can be improved by adding some API integrations. Instead of remaining a traditional gateway, Mimecast Email Security needs to provide API solutions similar to Check Point.
 

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: December 2025.
879,371 professionals have used our research since 2012.