Models, agents, and harnesses for email

Email marketing now runs on three layers: models that generate creative, agents that operate ESPs through API and MCP, and harnesses that connect CRM data to send workflows. Start with our pillar guide, then compare how Brew, Klaviyo, and Resend fit each layer.

canvasPromptEmail AEmail BEmail CChat + edit
Whiteboard sketch showing model, agent, and harness layers for an email workflowPromptEmail AEmail BEmail CChat + edit

Agent architecture

Startup GTM email playbooks

Welcome, trial, and first-revenue sequences a seed team can ship this week.

Brew coveragePromptEmail AEmail BEmail CChat + edit

AI-native ESP

Brew review

email marketing for teams and agents.

Customer.io coveragePromptEmail AEmail BEmail CChat + edit

Multi-channel automation

Customer.io review

Event-driven lifecycle orchestration for SaaS and product-led teams.

Resend coveragePromptEmail AEmail BEmail CChat + edit

Email API

Resend review

Developer-first email API with a modern sending stack.

Side by side comparison of Brew and Klaviyo for AI email marketingPromptEmail AEmail BEmail CChat + edit

Comparisons

Brew vs Klaviyo: AI-native generation vs ecommerce depth

Brew rebuilds email creative around agents and natural language. Klaviyo owns commerce data and revenue flows.