According to Live Direct Marketing's daily Tranco top-1M scan (September 22, 2026), the top 1 million websites route email through 264 identifiable email service provider (ESP)s. The largest is Amazon SES at 6.22% of SPF-publishing domains. This page ranks them all and links to a full guide for each.
Key facts
264 email service provider (ESP)s tracked across 637,585 SPF-publishing domains (Tranco top-1M, 2026-09-22).
Largest: Amazon SES — 6.22% of SPF-publishing domains.
Combined share of all tracked email service provider (ESP)s: 63.0%.
Every row links to a data-backed guide; figures update daily.
An ESP — email service provider — is the platform a domain uses to send at scale: transactional receipts, marketing campaigns, notifications. Unlike mailbox providers, ESPs are visible not in MX records but in SPF: the include: mechanisms a domain authorizes to send on its behalf. Counting those includes across the top 1M reveals the real market share of the sending industry.
The leaderboard is a story of two models. Developer-first APIs — Amazon SES, SendGrid, Mailgun, Postmark — win on transactional volume and now underpin a large fraction of the internet's automated mail. Marketing suites — Mailchimp, HubSpot, Salesforce — win on campaigns and CRM integration. Many domains authorize several at once, which is why the combined share of tracked ESPs runs well above any single leader.
Top bulk-sending ESPs by share of SPF-publishing domains (updated daily).
Full ranking — all 264 email service provider (ESP)s
Share = % of SPF-publishing domains in the Tranco top-1M. Click any name for its full guide.
Shared sending infrastructure is a double-edged sword. A reputable ESP gives you warm IP pools and established relationships with the mailbox providers — but you also inherit the reputation of every other sender on the same IPs. That is why two senders on the same ESP can see very different inbox rates, and why authentication (SPF alignment, DKIM signing, a DMARC policy) matters more, not less, when you send through a big platform. The co-usage data on each provider's guide shows which ESPs and mailbox providers cluster together in practice.
Are your emails landing in spam? Run a free inbox-placement test across Gmail, Outlook, Yahoo and more — see exactly where your mail lands and why.
What is the most-used email service provider (ESP) in 2026?
Amazon SES is the most common email service provider (ESP) in the Tranco top-1M, used by 39,679 domains (6.22% of SPF-publishing domains) as of September 22, 2026.
How many email service provider (ESP)s are there in the top 1M?
Live Direct Marketing's scan identifies 264 distinct email service provider (ESP)s with at least a handful of domains each, as of 2026-09-22.
