How AgentMail launched on X

AgentMail is an email inbox API for AI agents (YC S25). Developers use it to give each agent a persistent address that can send, receive, thread, and reply, with webhooks on inbound mail, without connecting a human Gmail account. For production sending, the company points teams to a custom domain so they own sender reputation and mail comes from their brand rather than agentmail.to. Domain Connect, announced by cofounder and CTO Michael Kim, covers the DNS step that custom domains require. That set is a receiving MX, a MAIL FROM MX for bounces, and TXT records for SPF, DKIM, and DMARC. When the DNS provider supports the Domain Connect standard and carries AgentMail's template, the setup-link endpoint returns a signed URL. The domain owner signs in at the provider, reviews the records, and the provider writes them. If the host does not support Domain Connect, those records still have to be added by hand. The API also reports a conflicting provider when the domain already has another service's MX records, such as Google Workspace, because applying the template would replace them. Custom domains are available on the Developer plan and above.