Email Service Provider (ESP)

An Email Service Provider (ESP) is a company that sends email on behalf of its customers as a managed service, typically via an API or campaign tools. Examples include SendGrid, Mailgun, Braze, and Amazon SES. An ESP operates its own MailOps stack (MTAs, IP pools, reputation management) so its customers don't have to. The build-vs-rent decision between running your own MTA and using an ESP is one of the central economic questions in email infrastructure.