ESP (Email Service Provider)

An ESP (Email Service Provider) is a platform that provides the infrastructure and tools for sending bulk email, managing subscriber lists, designing email templates, and tracking delivery metrics. Major ESPs include Mailchimp, Klaviyo, Beehiiv, ConvertKit (Kit), SendGrid, Brevo, Ghost, ActiveCampaign, and Campaign Monitor. In newsletter advertising, the ESP is responsible for sending emails to subscribers; the ad server (like MailAdx) is a separate layer that handles ad decisioning at open time. The integration between an ESP and MailAdx requires: (1) adding an email-hash merge tag to the ESP template, and (2) embedding MailAdx's ad tag in the template's HTML. No webhook or send-pipeline changes are needed.