According to Live Direct Marketing's daily Tranco top-1M scan (July 12, 2026), Mimecast is the email service provider (ESP) for 8,748 domains — 1.42% of 617,244 SPF-publishing domains. Detection method: include: mechanisms in the SPF record.
Mimecast is a cloud-based email security and management platform that organisations deploy to provide email archiving, business continuity, compliance, and threat detection capabilities. It integrates into recipient organisations' mail infrastructure as a processing layer, scanning and filtering incoming messages before they reach end-user inboxes.
Mimecast adoption across the web skews towards mid-market and smaller-to-medium organisations rather than the largest global enterprises, with particularly strong presence among .com-registered domains and concentrated in North America relative to other regions. For email senders and deliverability teams, this distribution matters significantly: organisations using Mimecast introduce stricter technical requirements and additional filtering rules into the delivery path, where sender authentication strength, message reputation, and policy compliance determine whether mail is delivered, delayed, quarantined, or rejected.
| Tranco rank band | Domains | Share of its base |
|---|---|---|
| Top 1,000 | 9 | 0.1% |
| Top 10,000 | 104 | 1.2% |
| Top 100,000 | 1,184 | 13.5% |
| Top 1,000,000 | 6,908 | 79.0% |
| Unranked | 543 | 6.2% |
| TLD | Domains | Share | |
|---|---|---|---|
| .com | 5,136 | 58.7% | |
| .org | 732 | 8.4% | |
| .co.uk | 537 | 6.1% | |
| .com.au | 294 | 3.4% | |
| .co.za | 243 | 2.8% | |
| .net | 160 | 1.8% | |
| .org.uk | 141 | 1.6% | |
| .de | 109 | 1.2% | |
| .edu | 95 | 1.1% | |
| .gov | 91 | 1.0% |
Cross-tabulated from the same daily snapshot — the other email services seen on the same 8,748 domains.
| Type | Service | Domains | Share of Mimecast users |
|---|---|---|---|
| Mailbox | Mimecast | 7,239 | 82.8% |
| Mailbox | Microsoft 365 | 816 | 9.3% |
| Mailbox | Proofpoint | 189 | 2.2% |
| Mailbox | Google Workspace | 168 | 1.9% |
| Mailbox | Unknown / Other | 69 | 0.8% |
| Mailbox | Self-Hosted | 33 | 0.4% |
| ESP | Salesforce | 1,311 | 15.0% |
| ESP | SendGrid (Twilio) | 1,149 | 13.1% |
| ESP | Amazon SES | 1,099 | 12.6% |
| ESP | HubSpot | 909 | 10.4% |
When an organisation deploys Mimecast, SPF records typically include Mimecast-operated IP ranges to authorise inbound mail processing. Senders targeting Mimecast-protected recipients face a two-stage authentication gauntlet: first the initial SPF check at the recipient's mail server, then deeper policy enforcement within Mimecast's own filtering engine. Mimecast performs DKIM and DMARC alignment validation, reverse DNS checks, and content analysis; senders with weak or absent authentication (particularly DKIM signatures or DMARC policies) risk being flagged as suspicious even if they clear baseline SPF validation. This means organisations using Mimecast impose stricter technical requirements on senders than organisations with simpler email stacks.
See the full Mimecast data page (KPI cards, trend, sample domains) →
If your recipients include organisations running Mimecast, your mail undergoes that platform's security scanning and policy enforcement before reaching users' inboxes. Testing against Mimecast-protected domains reveals whether your sender authentication, message content, and reputation survive Mimecast's filtering rules—which often exceed the strictness of basic mail server policies.
8,748 domains in the Tranco top-1M use Mimecast as their email service provider (ESP) as of July 12, 2026 (1.42% of SPF-publishing domains), according to Live Direct Marketing's daily DNS scan.
Mimecast accounts for 1.42% of SPF-publishing domains in the top 1M. Whether you should seed a test mailbox there depends on how much of your audience it represents — the co-usage table above shows the services it appears alongside most.
Mimecast is declining — its share moved -0.02 pp over the last 30 days (as of July 12, 2026).
Mimecast's largest TLD is .com (58.7% of its domains); it appears across 175 TLDs in total.