Customer.io email provider statistics and deliverability context
← Email Stats homeesp
According to Live Direct Marketing's daily Tranco top-1M scan (September 14, 2026), Customer.io is the email service provider (ESP) for 458 domains — 0.07% of 637,677 SPF-publishing domains. Its strongest TLD is .com (68.6% of its domains). Detection: include: mechanisms in the SPF record.
Last updated from the 2026-09-14 DNS snapshot.
What Customer.io represents in this dataset
Lifecycle marketing automation for product teams.
Directory category: Esp. The classification comes from include: mechanisms in the SPF record. It describes observed DNS infrastructure, not a commercial relationship and not the placement of any individual message.
What the 2026-09-14 snapshot shows about Customer.io
Across 49 distinct TLDs its top three are .com (68.6%), .io (5.2%), .casino (2.2%) — together 76.0% of the 458 domains, which makes the footprint narrow — three TLDs cover most of it, which is typical of a regional or single-market operator. The service most often observed on the same domains is Google Workspace (Mailbox, 356 domains, 77.7% of them), followed by Microsoft 365 (7.0%). Directly comparable by the same detection rule: Amazon SES, SendGrid (Twilio), Mailgun. Ranking between them reflects what is published in DNS, not delivery quality or volume sent. All figures come from a single daily DNS snapshot (2026-09-14); a domain appears here when its published records match the include: mechanisms in the SPF record rule, which is an infrastructure fact, not a commercial relationship.
Commonly used together with Customer.io
What else the same 458 domains use — cross-tabulated from the same daily snapshot (2026-09-14).
| Type | Service | Domains | Share of Customer.io users |
|---|---|---|---|
| Mailbox | Google Workspace | 356 | 77.7% |
| Mailbox | Microsoft 365 | 32 | 7.0% |
| Mailbox | Unknown / Other | 14 | 3.1% |
| Mailbox | Self-Hosted | 12 | 2.6% |
| Mailbox | Generic / unmatched (mail.*) | 10 | 2.2% |
| Mailbox | Generic / unmatched (mx*.*) | 7 | 1.5% |
| ESP | Zendesk | 106 | 23.1% |
| ESP | Mandrill | 77 | 16.8% |
| ESP | SendGrid (Twilio) | 70 | 15.3% |
| ESP | Amazon SES | 67 | 14.6% |
TLD distribution (top 30 of 49)
Frequently asked questions
How many domains use Customer.io?
458 domains in the Tranco top-1M use Customer.io as their email service provider (ESP) as of September 14, 2026, according to Live Direct Marketing's daily DNS scan.
What is Customer.io's market share?
Customer.io holds 0.07% of SPF-publishing domains in the Tranco top-1M (snapshot of 2026-09-14). The number is recomputed every day.
What are the biggest alternatives to Customer.io?
The largest email service provider (ESP)s in the same category by Tranco top-1M share are: Amazon SES, SendGrid (Twilio), Mailgun, Zendesk, Mailchimp (as of 2026-09-14).
Largest email service provider (ESP)s in this category
Amazon SES (6.16%) · SendGrid (Twilio) (4.62%) · Mailgun (4.00%) · Zendesk (3.75%) · Mailchimp (3.57%) · Mandrill (3.24%) · HubSpot (3.11%) · Salesforce (2.54%) · Mailjet (Sinch) (2.12%) · Cloudflare Email Routing (1.95%)
Domain sample (top 100 by Tranco rank)
Showing 100 of 458 domains.