According to Live Direct Marketing's daily Tranco top-1M scan (July 13, 2026), StackMail is the email service provider (ESP) for 1,097 domains — 0.18% of 617,702 SPF-publishing domains. Detection method: include: mechanisms in the SPF record.
StackMail is an email service provider observed in SPF records across the Tranco top-one-million websites through its include mechanisms. The service's footprint is concentrated amongst smaller and mid-market sites rather than the largest brands, and predominantly exists within the .com namespace.
For email professionals, this distribution pattern has important implications: StackMail's infrastructure serves a diffuse, high-diversity sender base rather than a consolidated pool of large operations. As a result, shared reputation signals associated with StackMail are fragmented rather than heavily weighted by a few major publishers. Those evaluating StackMail for sending, or monitoring inbound mail from StackMail-hosted sources, should treat collective reputation metrics as one input amongst many rather than a primary driver of their assessment.
| Tranco rank band | Domains | Share of its base |
|---|---|---|
| Top 1,000 | 0 | 0.0% |
| Top 10,000 | 0 | 0.0% |
| Top 100,000 | 24 | 2.2% |
| Top 1,000,000 | 576 | 52.5% |
| Unranked | 497 | 45.3% |
| TLD | Domains | Share | |
|---|---|---|---|
| .com | 585 | 53.3% | |
| .co.uk | 164 | 14.9% | |
| .org | 59 | 5.4% | |
| .net | 42 | 3.8% | |
| .uk | 26 | 2.4% | |
| .org.uk | 24 | 2.2% | |
| .site | 19 | 1.7% | |
| .in | 9 | 0.8% | |
| .info | 9 | 0.8% | |
| .ma | 8 | 0.7% |
Cross-tabulated from the same daily snapshot — the other email services seen on the same 1,097 domains.
| Type | Service | Domains | Share of StackMail users |
|---|---|---|---|
| Mailbox | StackMail (UK mailbox) | 915 | 83.4% |
| Mailbox | Microsoft 365 | 72 | 6.6% |
| Mailbox | Google Workspace | 62 | 5.7% |
| Mailbox | Self-Hosted | 17 | 1.5% |
| Mailbox | Unknown / Other | 7 | 0.6% |
| Mailbox | Barracuda | 3 | 0.3% |
| ESP | MailerSend | 23 | 2.1% |
| ESP | Mailchimp | 19 | 1.7% |
| ESP | Mailgun | 14 | 1.3% |
| ESP | Mandrill | 12 | 1.1% |
StackMail's distribution across a broad base of smaller and mid-market senders means that any shared sender reputation associated with its infrastructure is built from high-diversity, lower-concentration sending behaviour. This fragmentation makes shared reputation metrics less predictive for individual StackMail users than might be the case for ESPs serving primarily consolidated, large-scale operations. If you operate a domain through StackMail, your sender reputation is built primarily at the domain level rather than benefiting from a large, tightly-managed collective pool—making domain authentication, content quality, and sending practices essential rather than ancillary to your deliverability outcomes.
See the full StackMail data page (KPI cards, trend, sample domains) →
Testing is worthwhile if StackMail is material to your recipient base or sending infrastructure, but should be proportional to your actual exposure rather than treated as a universal test case.
1,097 domains in the Tranco top-1M use StackMail as their email service provider (ESP) as of July 13, 2026 (0.18% of SPF-publishing domains), according to Live Direct Marketing's daily DNS scan.
StackMail accounts for 0.18% 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.
StackMail's largest TLD is .com (53.3% of its domains); it appears across 88 TLDs in total.