Email service provider (ESP)
Software that sends, tracks, and manages bulk email — Mailchimp, Klaviyo, HubSpot, Resend, Postmark, SendGrid.
An email service provider (ESP) is software that handles the infrastructure of sending, tracking, and managing email at scale. ESPs maintain dedicated sending IPs, manage authentication (SPF/DKIM/DMARC) per customer domain, queue and dispatch messages, deduplicate against suppression lists, capture engagement webhooks, and report aggregate metrics.
The ESP market spans transactional (Postmark, SendGrid, Resend, Mailgun, Amazon SES) — high deliverability, per-message API — and lifecycle/marketing (Mailchimp, Klaviyo, HubSpot, Customer.io) — visual editors, segmentation, A/B testing, automation flows. Customers often run both: transactional for receipts and password resets, lifecycle for newsletters and drips.
We are explicitly not an ESP. The product generates the copy that goes into the ESP. Our public API and CSV export let customers wire our output directly into whatever ESP they already use, so they get the conversion benefits without changing their delivery stack.