Sendmux

Sendmux gives an AI agent or application a workspace for sending, receiving and monitoring email. The product overview describes dedicated mailboxes, structured message content and routing across sending providers.

Give the agent a bounded inbox

You can create mailboxes on a verified custom domain or the shared myagent.mx domain. Sendmux describes a clean JSON content view that strips signatures and quoted history by default, with links, headers and attachment metadata available on request. An agent can therefore read the new reply without treating an entire previous conversation as fresh instructions.

Its setup documentation separates sending, management and mailbox credentials. Choose the access the agent needs and keep permission to send narrower than permission to read whenever your workflow allows. A sender's message is untrusted input; it should not authorize the agent to disclose another thread or change account settings.

Connect incoming events to controlled actions

Sendmux lists signed webhooks, server-sent events for live mailbox clients and change polling for resynchronizing state. Outbound messages can use HTTP or SMTP, and HTTP sends support idempotency keys for retry handling. A queued message ID confirms queuing, not that the recipient has received or read the email.

Start with a test mailbox and a known recipient. Check the reply destination, attachment handling and event signature verification before enabling automatic replies. Set a clear escalation path for messages the agent cannot interpret, and avoid letting an incoming email grant itself new authority.

The documentation says managed Amazon SES is for transactional email only. Marketing, newsletters and bulk promotional sends require your own provider. Provider routing and quotas do not remove those usage restrictions.

Estimate recipients and storage, not seats

The pricing page lists Free with two mailboxes, one domain and one dollar of usage credit. Pro adds a seven-dollar monthly team fee plus prepaid usage, without per-seat or per-mailbox fees.

Connected outbound and inbound each list a rate of fifty cents per thousand accepted recipients or distinct mailbox deliveries; managed sending lists seventy-five cents per thousand accepted recipients. Each accepted To, CC or BCC recipient counts separately. Pro's advertised unlimited capacity remains subject to fair usage, approval for resource increases and provider quotas. Include those limits and storage charges when estimating a production workflow.