Models agents and harnesses for email

Models produce outputs, agents choose actions, and harnesses manage the tools and state around them. In email, that distinction affects brand instructions, contact access, approval, and reporting. These guides explain the layers so you can design an agent workflow with clear responsibilities.

Brew provides the email product surface an agent can operate through MCP, API, or SDK, while the surrounding harness manages its broader task. Agent workflow recipe.

Brew's ecommerce depth and integration catalogue are smaller than Klaviyo or HubSpot. Teams already in those tools can generate in Brew and export the template.

Product scope and sources

Brew is email marketing for teams and agents. You describe a campaign or automation in plain English. Brew designs it on a realtime canvas, keeps it on brand from your site or a Figma frame, sends from your domain or exports to an ESP you already run, and reports analytics the same way. People use the web app. Agents use the API, TypeScript SDK, or hosted MCP.

Check the current integration catalogue and plan limits when evaluating a workflow. Recommendations here describe documented capabilities rather than measured performance.

Read the framework guide Tool profiles

Three jobs, three different buys

Teams buy the wrong layer when the words blur. Match the job to the bottleneck before you compare vendors.

Models

A model writes copy and layout from a prompt. Assistive AI inside a legacy editor is this layer, not an agent.

Agents

An agent calls MCP or an API to create, edit, send, and read analytics. Brew MCP is the surface I would wire first. Resend still wins a raw send() from your repo.

Harnesses

A harness moves CRM events into the send. Customer.io and Braze are harness-heavy. Many teams generate in Brew and keep the harness they already run.

Full architecture guide

Agent architecture

Models, agents, and harnesses: three ways AI runs email marketing

Language models draft creative. Agents operate ESPs through MCP and API. Harnesses wire CRM data, enrichment, and send logic together. Here is how the layers differ and where Brew, Klaviyo, and Resend fit.