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Email security · October 2026 Edition
Microsoft Defender for Office 365 vs Mimecast Email Security
Three of fourteen models named Microsoft Defender for Office 365 first on the direct prompt; one named Mimecast Email Security. Both were named by all fourteen models and Microsoft Defender for Office 365 carries 51 labels and Mimecast Email Security 50, so the shares are not directly comparable.
Named in three categories this edition.
Named in one category this edition.
First-choice share32%10%Of first choices across the direct, paraphrase, budget and scale prompts, 0 to 100.
Negative rate6%22%Negative labels as a share of the product's labels, 0 to 100.
Rank in category#1#3A position in a field of 9; printed, not drawn.
Labels5150A count; the two differ.
The two percentage rows are drawn on one 0 to 100 track, Microsoft Defender for Office 365 reading right to left. Rank and label count are printed, not drawn.Proofpoint Email Protection was named alongside these two in nine of the fourteen direct answers. Microsoft Defender for Office 365 vs SpamTitan · Microsoft Defender for Office 365 vs Barracuda Email Protection · Microsoft Defender for Office 365 vs Proofpoint Email Protection
Share is the count of first choices across the direct, paraphrase, budget and scale prompts over all fourteen models, for a mid-market B2B company; rank is within the category; every quote names the model and the prompt it came from. Both figures come from the email security page.
By framing
How many of the fourteen models made each the first choice, per way of asking, and how many argued against it.
Microsoft Defender for Office 365First choices, of fourteen modelsMimecast Email Security
Direct313 against Mimecast Email Security
Paraphrase741 against Mimecast Email Security
Comparative21
Budget-constrained502 against Mimecast Email Security
Scale-constrained101 against Mimecast Email Security
Negative013 against Microsoft Defender for Office 365 · 4 against Mimecast Email Security
Bars are first choices, 0 to 14 each sideModels that argued againstA model can name both, so the two sides of a row do not sum to fourteen.
Across every category in the October 2026 Edition, Microsoft Defender for Office 365 and Mimecast Email Security were named in the same answer 120 times, of the 176 answers naming Microsoft Defender for Office 365 and the 162 naming Mimecast Email Security. In those answers Mimecast Email Security took the first choice nine times and Microsoft Defender for Office 365 forty.
Every model, every framing
The eighty-four answers behind the chart above, one cell each: where Microsoft Defender for Office 365 and Mimecast Email Security stood in it.
| Model | Direct | Paraphrase | Comparative | Budget-constrained | Scale-constrained | Negative |
|---|---|---|---|---|---|---|
| Claude Haiku 4.5 | | | | |||
| GPT-5.4 mini | | | | | ||
| Gemini 3.5 Flash | | | | | | |
| Perplexity Sonar | | | | |||
| Grok 4.1 Fast | | | | | ||
| Mistral Small | | | | |||
| DeepSeek V4 Flash | | | | | | |
| Llama 4 Maverick | | |||||
| Qwen 3.7 Flash | | | | | | |
| Kimi K2 | | | | | ||
| GLM 4.7 FlashX | | | | | | |
| MiniMax M2.5 | | | | |||
| GPT-6 Luna | | | | | | |
| Muse Glimmer 30B | | | | | | |
Microsoft Defender for Office 365 Mimecast Email Security first choice named as an alternative argued againstblank: not namedEach cell is one answer, Microsoft Defender for Office 365 on the left and Mimecast Email Security on the right.The direct prompt
The plain question, one answer per model, grouped by where Microsoft Defender for Office 365 and Mimecast Email Security stood in it.
Microsoft Defender for Office 365 first, Mimecast Email Security an alternative
3 of 14 modelsMimecast Email Security was named in the answer but not as the choice, or not at all.GPT-5.4 miniMicrosoft Defender for Office 365 alternatives: Abnormal AI, Mimecast Email Security, Proofpoint Email Protection
Perplexity SonarMicrosoft Defender for Office 365 alternatives: Check Point Harmony Email & Collaboration, Mimecast Email Security
GLM 4.7 FlashXMicrosoft Defender for Office 365 alternatives: Abnormal AI, Barracuda Integrated Email Protection, IRONSCALES, Proofpoint Email Protection
Mimecast Email Security first, Microsoft Defender for Office 365 not the choice
1 of 14 modelsMicrosoft Defender for Office 365 was named in the answer but not as the choice, or not at all.MiniMax M2.5Check Point Harmony Email & Collaboration, Mimecast Email Security
Neither was the first choice, one was named
8 of 14 modelsThe answer put something else first and named one of the two as an alternative.Claude Haiku 4.5Barracuda Email Protection alternatives: IRONSCALES, Mimecast Email Security, Proofpoint Email Protection
Grok 4.1 FastProofpoint 365 Total Protection alternatives: Abnormal AI, Mimecast Email Security
Mistral SmallCheck Point Harmony Email & Collaboration, Proofpoint Email Protection alternatives: Mimecast Email Security, Symantec Email Security.cloud
DeepSeek V4 FlashAbnormal AI alternatives: Check Point Harmony Email & Collaboration, Microsoft Defender for Office 365, Proofpoint Email Protection
Qwen 3.7 FlashProofpoint Email Protection alternatives: Abnormal AI, IRONSCALES, Microsoft Defender for Office 365
Kimi K2IRONSCALES alternatives: Abnormal AI, Mimecast Email Security, Proofpoint Email Protection
GPT-6 LunaAbnormal AI alternatives: Microsoft Defender for Office 365, Mimecast Email Security, Proofpoint Email Protection
Muse Glimmer 30BProofpoint Email Protection alternatives: Abnormal AI, Barracuda Email Protection, Check Point Harmony Email & Collaboration, Guardian Digital, Microsoft Defender for Office 365, ThreatDown Email Security, Trustifi
Neither was named
2 of 14 modelsThe answer made no first choice from these two in this category.Gemini 3.5 FlashCheck Point Harmony Email & Collaboration alternatives: Abnormal AI, Barracuda Email Protection, IRONSCALES
Llama 4 Maverickno first choice
Bold names in an answer are the products the judge labeled a first choice; a model naming several gives each of them that label. The full answer text for every row is in the record.
By buyer segment
The same question asked on behalf of a different buyer. Each standing is computed within its segment and they are never added together. The figures above are the mid-market standing, which is the one the category orders by.
Small business
Microsoft Defender for Office 365 leads by twenty-three points.
Microsoft Defender for Office 36527%#1 of 10Mimecast Email Security4%#8 of 10Mid-marketThe figures above
Microsoft Defender for Office 365 leads by twenty-two points.
Microsoft Defender for Office 36532%#1 of 9Mimecast Email Security10%#3 of 9Enterprise
Microsoft Defender for Office 365 leads by twenty-one points.
Microsoft Defender for Office 36529%#2 of 8Mimecast Email Security8%#4 of 8What the models said about Microsoft Defender for Office 365
Every negative label with a quote, up to three, then the highest-weighted positives, up to three. Six of seven in this category shown.
“Microsoft's published comparison, for example, uses different "missed threat" criteria for Defender than for competing gateways, so it shouldn't be treated as a neutral head-to-head ranking.” GPT-6 Luna · negative prompt · soft negative
“strong execution but limited vision for evolving threats. Complaints include high false positives, poor internal email scanning” Grok 4.1 Fast · negative prompt · soft negative
“relying *solely* on native cloud email security is a risk for organizations with high threat profiles” Gemini 3.5 Flash · negative prompt · soft negative
“Microsoft Defender for Office 365 is the default choice for most Microsoft-365 shops—it's deeply integrated, cost-effective, and provides a solid baseline.” GLM 4.7 FlashX · comparative prompt · first choice
“Start with what you already have — if you're on Microsoft 365 E5, check if Defender for O365 Plan 2 is already included before paying for a new platform.” DeepSeek V4 Flash · scale prompt · first choice
“Microsoft Defender for Office 365 is the most pragmatic starting point—low cost, deep integration, and solid baseline protection.” GLM 4.7 FlashX · direct prompt · first choice
What the models said about Mimecast Email Security
Every negative label with a quote, up to three, then the highest-weighted positives, up to three. Six of eight in this category shown.
“shifted heavily away from traditional, complex Secure Email Gateways (SEGs like traditional configurations of Proofpoint or Mimecast)” Gemini 3.5 Flash · paraphrase prompt · soft negative
“Traditional gateways (like classic Mimecast or Proofpoint setups) ... can be complex to set up, can disrupt mail flow if they fail” Gemini 3.5 Flash · scale prompt · soft negative
“moved away from legacy, complex Secure Email Gateways (SEGs) that require changing MX records (such as Proofpoint or Mimecast)” Gemini 3.5 Flash · direct prompt · soft negative
“Mimecast is the usual mid-market pick. The unified contract simplifies procurement and it's explicitly positioned for small- and mid-sized businesses.” Muse Glimmer 30B · paraphrase prompt · first choice
“Prioritize Gartner Leaders: Proofpoint, Abnormal Security, Mimecast, Trend Micro, Check Point, Egress/KnowBe4. They score highest” Grok 4.1 Fast · negative prompt · first choice
“Widely considered the market leader, Mimecast focuses on reliability and data resilience.” Qwen 3.7 Flash · comparative prompt · first choice
Also compared
Microsoft Defender for Office 365 vs SpamTitanMicrosoft Defender for Office 365 vs Barracuda Email ProtectionMicrosoft Defender for Office 365 vs Proofpoint Email ProtectionMicrosoft Defender for Office 365 vs Check Point Harmony Email & CollaborationMicrosoft Defender for Office 365 vs Abnormal AIMicrosoft Defender for Office 365 vs IRONSCALESSpamTitan vs Mimecast Email SecurityMimecast Email Security vs Barracuda Email ProtectionMimecast Email Security vs Proofpoint Email ProtectionMimecast Email Security vs Check Point Harmony Email & CollaborationMimecast Email Security vs Abnormal AIMimecast Email Security vs IRONSCALESAll twenty-eight head-to-head pages and the full email security standing
Comparisons are drawn for the top eight products in each category, each against each. The output is the models' output; nothing here is a recommendation by the index.