emSMTP email service provider (ESP)
According to Live Direct Marketing's daily Tranco top-1M scan (September 24, 2026), emSMTP is the email service provider (ESP) for 139 domains — 0.02% of 637,420 SPF-publishing domains. Detection method: include: mechanisms in the SPF record.
Key facts
- 139 domains in the Tranco top-1M use emSMTP (0.02% of SPF-publishing domains).
- Snapshot date: 2026-09-24 — recomputed every day.
- Strongest TLD: .com (25.9% of its domains).
- Most co-used service: Microsoft 365.
- Directory category: email service provider.
Why emSMTP appears in this category
emSMTP — transactional/marketing relay.
We classify it as a email service provider from include: mechanisms in the SPF record matching a maintained provider rule. This is infrastructure attribution from public DNS, not evidence of a direct contract or exclusive use.
emSMTP is an email relay service that accepts SMTP connections and delivers messages to recipient mail servers on behalf of sending organisations. It provides mail delivery infrastructure for senders who choose to route messages through its platform.
Across the public internet, emSMTP appears predominantly in the SPF records of smaller and mid-market organisations, rather than among the largest global brands. Its deployment is internationally distributed across many top-level domains, concentrated primarily in .com addresses, and it frequently appears alongside Microsoft 365 mail infrastructure. For deliverability purposes, emSMTP is a routinely deployed relay service in the mid-market segment; its presence in SPF records reflects a standard infrastructure choice rather than a reputation concern.
Where emSMTP sits in the Tranco ranking
| Tranco rank band | Domains | Share of its base |
|---|---|---|
| Top 1,000 | 0 | 0.0% |
| Top 10,000 | 0 | 0.0% |
| Top 100,000 | 34 | 24.5% |
| Top 1,000,000 | 105 | 75.5% |
| Unranked | 0 | 0.0% |
Top-level domain split
| TLD | Domains | Share | |
|---|---|---|---|
| .com | 36 | 25.9% | |
| .de | 35 | 25.2% | |
| .at | 10 | 7.2% | |
| .ch | 8 | 5.8% | |
| .co.uk | 8 | 5.8% | |
| .it | 4 | 2.9% | |
| .nl | 4 | 2.9% | |
| .com.au | 3 | 2.2% | |
| .ru | 3 | 2.2% | |
| .net | 3 | 2.2% |
What emSMTP users also use
Cross-tabulated from the same daily snapshot — the other email services seen on the same 139 domains.
| Type | Service | Domains | Share of emSMTP users |
|---|---|---|---|
| Mailbox | Microsoft 365 | 58 | 41.7% |
| Mailbox | Google Workspace | 27 | 19.4% |
| Mailbox | Unknown / Other | 12 | 8.6% |
| Mailbox | Generic / unmatched (mx*.*) | 9 | 6.5% |
| Mailbox | Self-Hosted | 6 | 4.3% |
| Mailbox | Generic / unmatched (mail.*) | 5 | 3.6% |
| ESP | Emarsys (SAP) | 117 | 84.2% |
| ESP | Zendesk | 20 | 14.4% |
| ESP | Amazon SES | 18 | 12.9% |
| ESP | Mailjet (Sinch) | 11 | 7.9% |
emSMTP in multi-relay SPF configurations
When emSMTP appears in a domain's SPF record, it is explicitly authorised as a mail relay for that sender. The prevalence of emSMTP alongside Microsoft 365 configurations indicates that many mid-market organisations authorise multiple relays within their mail infrastructure, a deployment pattern that carries no inherent deliverability risk provided all authorised relays maintain clean sending practices and sender reputation. Organisations supporting multiple relays should ensure their SPF records remain concise and regularly audit which relays remain active, as unnecessary include mechanisms increase complexity and potential attack surface.
See the full emSMTP data page (KPI cards, trend, sample domains) →
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Frequently asked questions
What is emSMTP?
emSMTP is an SMTP relay service that organisations can authorise to send mail on their behalf. It is commonly found deployed alongside Microsoft 365, indicating that many organisations use it as a supplementary mail relay within their broader mail infrastructure.
How many domains use emSMTP?
139 domains in the Tranco top-1M use emSMTP as their email service provider (ESP) as of September 24, 2026 (0.02% of SPF-publishing domains), according to Live Direct Marketing's daily DNS scan.
Is emSMTP common enough to affect email deliverability testing?
emSMTP accounts for 0.02% 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.
Which countries or TLDs use emSMTP most?
emSMTP's largest TLD is .com (25.9% of its domains); it appears across 30 TLDs in total.