Warmbox

For SDR/BDR teams, marketing ops, and agencies running cold email, Warmbox is a focused deliverability tool that does one thing — keeps your sender reputation healthy — and does it without requiring much ongoing configuration. On the agentic readiness front, there's no API available and MCP status is unknown, so you can't drive this from an agent without scraping; it's a UI-only tool, which limits how far you can embed it into an automated outbound stack. Pricing starts at $19/month for a single inbox, which is affordable for small teams, though costs stack up quickly if you're managing multiple domains or inboxes across a larger agency setup. The core limitation to know going in: Warmbox is warm-up infrastructure, not a sending platform — you'll need to pair it with a sequencer, and the value it delivers is entirely dependent on how disciplined your broader cold email hygiene is.