What is Email Service Provider (ESP)?
An Email Service Provider (ESP) is a company that offers email sending infrastructure, tools, and services, ranging from marketing email platforms to transactional email APIs.
An Email Service Provider (ESP) is any company that provides email sending infrastructure and services. The term covers a broad range of products, from marketing email platforms (Mailchimp, ActiveCampaign) to transactional email APIs (SendGrid, Postmark) to full email infrastructure providers.
ESPs handle the complex infrastructure needed to send email at scale: maintaining IP addresses, managing server reputation, handling bounces and complaints, ensuring deliverability, and providing analytics. Without an ESP, you'd need to manage your own mail servers, IP reputation, deliverability optimization, and compliance.
For SaaS platforms that need to send email on behalf of customers, a standard ESP may not be sufficient. Traditional ESPs are built for direct senders (one company sending their own email), not for platforms that need multi-tenant architecture, per-customer domain management, and tenant isolation.
Why Email Service Provider (ESP) Matters
Choosing the right ESP determines your deliverability, reliability, and development experience. For platforms, the choice is especially critical: most ESPs aren't built for multi-tenant use cases, and bolting multi-tenancy onto a single-sender ESP creates complexity, data mixing, and scaling headaches.
Frequently Asked Questions
What is an Email Service Provider?
An ESP is a company that provides email sending infrastructure. This ranges from marketing email platforms (Mailchimp, Brevo) to transactional APIs (SendGrid, Postmark) to platform-focused solutions (Ark). They handle the servers, IP reputation, and deliverability so you don't have to.
How do I choose an ESP for my SaaS platform?
If your SaaS sends email on behalf of customers, look for multi-tenant support, per-customer domain management, per-tenant suppression lists, and per-tenant analytics. Generic ESPs may work for simple use cases but create problems at scale when customers need scoped sending.
What's the difference between an ESP and an email API?
An ESP is the provider (the company and service). An email API is the integration method—the programmatic interface developers use to send email. Most modern ESPs offer an email API as their primary integration method, alongside SMTP.
Related Terms
Email API
An email API (Application Programming Interface) allows developers to send, receive, and manage emai...
SMTP
SMTP (Simple Mail Transfer Protocol) is the standard protocol for sending emails across the internet...
White Label Email
White label email is a service that lets platforms send email on behalf of their customers using the...
Transactional Email
Transactional emails are automated messages triggered by user actions, such as password resets, orde...
Email Deliverability
Email deliverability is the ability to successfully deliver emails to recipients' inboxes rather tha...
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