Customer.io email provider statistics and deliverability context
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According to Live Direct Marketing's daily Tranco top-1M scan (September 24, 2026), Customer.io is the email service provider (ESP) for 457 domains — 0.07% of 637,420 SPF-publishing domains. Its strongest TLD is .com (68.3% of its domains). Detection: include: mechanisms in the SPF record.
Last updated from the 2026-09-24 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 2026-09-24 snapshot shows about Customer.io
Across 48 distinct TLDs its top three are .com (68.3%), .io (5.5%), .co (2.4%) — together 76.1% of the 457 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, 357 domains, 78.1% 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 (2026-09-24); 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 457 domains use — cross-tabulated from the same daily snapshot (2026-09-24).
| Type | Service | Domains | Share of Customer.io users |
|---|---|---|---|
| Mailbox | Google Workspace | 357 | 78.1% |
| Mailbox | Microsoft 365 | 32 | 7.0% |
| Mailbox | Unknown / Other | 13 | 2.8% |
| Mailbox | Self-Hosted | 12 | 2.6% |
| Mailbox | Generic / unmatched (mail.*) | 10 | 2.2% |
| Mailbox | Generic / unmatched (mx*.*) | 6 | 1.3% |
| ESP | Zendesk | 105 | 23.0% |
| ESP | Mandrill | 75 | 16.4% |
| ESP | SendGrid (Twilio) | 71 | 15.5% |
| ESP | Amazon SES | 69 | 15.1% |
TLD distribution (top 30 of 48)
Frequently asked questions
How many domains use Customer.io?
457 domains in the Tranco top-1M use Customer.io as their email service provider (ESP) as of September 24, 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 2026-09-24). 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 2026-09-24).
Largest email service provider (ESP)s in this category
Amazon SES (6.23%) · SendGrid (Twilio) (4.68%) · Mailgun (4.01%) · Zendesk (3.77%) · Mailchimp (3.61%) · Mandrill (3.26%) · HubSpot (3.18%) · Salesforce (2.57%) · Mailjet (Sinch) (2.14%) · Cloudflare Email Routing (1.96%)
Domain sample (top 100 by Tranco rank)
Showing 100 of 457 domains.