Companies Using Mimecast

I've spent more than ten years building web crawling and technographic systems, and mail gateways are one of the few categories where our detection comes close to a census. Our October 2026 crawl finds 72,817 domains whose MX record sends inbound mail through Mimecast, and we matched 59,080 of them to a company. An MX record is live routing, so this is a list of domains whose mail passes through Mimecast today, not a list of old licences. Below I use that set, the switches we've logged since March 2026, an MX lookup on all 50 companies in the table, Mimecast's own FAQ, and the G2 review counts on this page.

Growth trajectory

The chart reads 60,614 domains in June and 72,817 in October, in two steps: 8,209 added into July and 3,103 into September, with almost nothing in between. Steps like that come from our side. The set of domains we crawl turns over every month, with dead sites dropping out and new ones added, and our detection widens over time. The flat months are the better read on demand, and they say the base is steady: 300 domains added in August, 591 in October. 2,818 domains have dropped Mimecast since March, under 4% of today's count.

"A company can forget to remove a tracking script. It can't forget where its email goes. So when an MX-based line stays flat, customers are staying put." - Mehmet Suleyman, CEO & Co-founder at TechnologyChecker

Sales Signal: This is a stable, renewal-driven base rather than a land grab. Timing matters more than volume here: work accounts around renewal, and treat the 2,818 recent drops as the live churn pool.

Customer profile

Mimecast's customers sit in the middle of the size range. 51.89% of matched companies have 11 to 200 staff, 25.71% have ten or fewer and 11.94% have more than 500. Microsoft 365's profile, by contrast, has 58.97% at ten or fewer: a separate gateway tends to start at the size where someone in IT owns email risk, which is also the buyer Mimecast's FAQ describes, organisations with lean IT and security teams. The base is old too. 41.41% were founded before 1990 and 16.8% before 1960. The top of the list is global groups, HP, CVS Health, Sanofi, Michelin, Emirates and the London Stock Exchange Group, and all 50 domains in the table pointed their MX at Mimecast when we checked on 10 October 2026. One that our data still ranked in the top 50 didn't: ppd.com now routes to Proofpoint, so we replaced it.

Sales Signal: The buyer is an IT manager at a company with 51 to 500 staff, compliance obligations and no dedicated email security engineer. Sell them time back rather than more controls.

Industry and geographic concentration

Financial services leads at 6.08%, then construction (4.92%), insurance (4.63%) and law practices (4.36%). Finance, insurance, accounting and the two legal labels add up to 18.88%, the regulated core Mimecast's own FAQ describes: archiving, retention and legal hold for FINRA, SEC 17a-4, HIPAA and GDPR. Construction is the outlier, and our data can't say why. Proofpoint's profile leans even further into finance, at 11.64%.

Geography is the most distinctive thing about this base. The United Kingdom has 14,962 matched companies against 29,809 in the United States, about one to two. Proofpoint's profile runs about one to eleven and Microsoft 365's about one to three. Mimecast was founded in London in 2003 and is still headquartered there. The United Arab Emirates (1,002) is the other surprise in the top six.

Sales Signal: Mimecast's UK base is unusually dense, so a UK seller of archiving, compliance or awareness tools will meet it on a large share of mid-sized accounts. A rival gateway should expect harder displacement work there than in the US.

Migration patterns

MX changes are real switches: inbound mail stops passing through one gateway and starts passing through the other. Two corridors pass our tests. Proofpoint took 266 domains from Mimecast and gave back 52 since March 2026, about five to one, with 48 of those losses in the last 30 days. Barracuda goes the other way: 160 domains came to Mimecast from Barracuda and 59 left for it, about 2.7 to one. In both pairs few domains keep both gateways, 20.3% for Proofpoint and 23% for Barracuda.

What I've taken out matters as much. Earlier versions of this page led with Microsoft 365 as Mimecast's main exit. Since March, 1,818 domains that dropped Mimecast show a Microsoft 365 MX, but 1,009 that dropped Microsoft 365's MX show Mimecast's, and 2,417 show both today. That fails both our direction test and our overlap test, so it isn't in the table. Hornetsecurity (11 one way, 8 the other) and Sophos (1,183 domains running both) are out for the same reasons.

"Proofpoint is the only rival taking Mimecast domains at a steady clip, about five for every one it loses. It's small next to a 72,817-domain base, but it's the corridor I'd watch." - Mehmet Suleyman, CEO & Co-founder at TechnologyChecker

Sales Signal: Two plays. Proofpoint has a measurable pull on Mimecast accounts, so migration and retention services around that corridor have real demand. Barracuda customers lean the other way, moving to Mimecast nearly three times as often as the reverse.

Technology ecosystem

Across the 73,192 live Mimecast domains our stack figures use, Google Analytics runs on 68.66% and WordPress on 46.21%, with Cloudflare in front of 48.33%. Microsoft 365 shows on only 3.3%, which says more about our detection than about the market. Our Microsoft 365 signal reads the MX record, and a Mimecast domain's MX points at Mimecast. Mimecast itself says it is especially well suited to companies on Microsoft 365, so the mailbox platform behind most of these domains is invisible to an MX read. Google Workspace, at 0.27%, is likely hidden the same way.

Sales Signal: Don't infer a Mimecast customer's mailbox platform from stack data. On these domains, a missing Microsoft 365 row tells you nothing about whether they use it.

G2 review signals

The G2 summary on this page counts 148 mentions across five positives, and blocking dominates: spam and malicious-email detection (40), security features (28), email protection (22) and spam blocking again (22), with ease of use at 36. The five complaints total 75. Three of them, 42 mentions between them, describe legitimate mail being held, missed or hard to find; the other two, complexity (17) and configuration effort (16), are about the admin load. That lines up with the Proofpoint corridor in one respect: a gateway that's hard to tune is a gateway that gets questioned at renewal, though our data can't show why any single domain left.

Sales Signal: Lead with tuning and admin time, not detection. Reviewers already rate Mimecast's blocking; their complaints are about what it blocks by mistake and how long it takes to set up.

Key takeaways

1. Mimecast routes mail for 72,817 domains, 9.48% of our Email Security table and more than any rival gateway charted here.
2. The base is steady: flat months between coverage steps, and 2,818 drops since March.
3. The core customer is a mid-sized, long-established company in finance, insurance or law, in the US or the UK.
4. Proofpoint is the one rival taking Mimecast domains steadily, about five to one, while Mimecast wins its exchange with Barracuda.
5. Microsoft 365 overlaps heavily and hides behind the MX record, so we don't count it as switching.

Sales applications

Outreach angle: "Your MX points at Mimecast, so your mail is filtered before it reaches your mailboxes. How much of your team's week goes on releasing held messages?" It goes straight at the most common review complaints.

Targeting strategy: UK and US companies with 51 to 500 staff in financial services, insurance or law. That's where the base is densest and where compliance budgets sit.

Competitive angle: the 160 domains that moved from Barracuda to Mimecast since March are recently migrated and likely still tuning their policies.

Every detection figure here comes from our crawl: 72,817 Mimecast domains and 59,080 matched companies as of October 2026. Our write-up on technology detection methods covers how we read DNS records like these.