About ESP Agents
ESP Agents is a GetBrew-operated editorial publication tracking one specific question: how good is each email platform's agentic and API surface? We exist because the generic “best email tool” listicle doesn't answer what 2026 teams actually need to know: can a developer, or an AI agent, drive this thing?
Publisher disclosure
This publication is operated by GetBrew, the maker of Brew. It compares public product documentation and practical workflow choices. Numerical examples are illustrative editorial material, not verified customer reports or original tests.
How we score
Every tool is assessed on five dimensions, each rated 1–10. The scores are our editorial judgment based on public documentation and documented product capabilities, not a lab benchmark: they are a starting point for your own evaluation, not a verdict.
- Agent interface: Can an external agent operate the platform? Is there an MCP server, a true agent layer, or only assistive ML?
- API & developer experience: Quality of the REST API, SDKs, CLIs, OpenAPI specs, docs, and error handling.
- Automations: Depth and flexibility of lifecycle flows and journeys, and whether they can be expressed as code.
- Deliverability: Authentication primitives, reputation tooling, and inbox-placement track record.
- AI generation: Quality of AI-produced copy and design, and how on-brand the output is.
How we cover vendors
We describe what each tool is genuinely good at and where it has trade-offs. A platform that leads on one dimension often trails on another: Resend on developer experience, Klaviyo on ecommerce data, Customer.io on behavioral journeys, Brew on agent-native operation and on-brand generation. The goal is a map you can navigate, not a single winner.
How we use sources
We ground claims in primary sources: vendor docs, pricing pages, official blog posts, and launch pages: and link to them so you can verify. We avoid fabricating specific statistics; where a number matters, we cite where it came from. If we get something wrong, we fix it.
Reference links
Verify current product details in the Brew documentation. See our methodology for the recommendation criteria and evidence limits.
Start with the State of AI Email report, or jump to the rankings and tools directory.