What’s the difference between SMTP, IMAP, and POP3?

An Email Service Provider is a company that provides infrastructure and tools for sending bulk email, typically for marketing, transactional, and communication purposes. ESPs handle the technical complexity of email delivery at scale, including server infrastructure, IP reputation management, authentication setup, bounce processing, and compliance with email regulations. They enable businesses to send thousands or millions of emails without building and maintaining their own email infrastructure.

ESPs offer varying levels of service and functionality. Basic ESPs provide sending infrastructure with minimal features. Marketing-focused ESPs add campaign management, templates, segmentation, automation, and analytics. Enterprise platforms include advanced personalization, multi-channel integration, dedicated infrastructure, and sophisticated deliverability services. The right choice depends on your volume, complexity, and technical capabilities.

The ESP market includes well-known names like Mailchimp, Klaviyo, Braze, Salesforce Marketing Cloud, and many others, each with different strengths, price points, and target customers. Some specialize in specific industries or company sizes while others aim for broad applicability. Choosing an ESP is one of the most important infrastructure decisions for any email program because it affects deliverability, capabilities, and operational efficiency.