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Hit the Free MCP send or mailbox limit? Here’s the upgrade path

You’re on Free. The agent is working. Then MCP returns a limit error — daily send cap, or “you already have your one mailbox.” That’s expected. Free is sized for a personal agent with guardrails; when you outgrow it, the path is in-product Upgrade, not a support ticket.

Upgrade to Starter → Create Free account →

Assistant Mail = allowlist + recipient consent — SSH-keys-for-email. Caps exist so a runaway tool call doesn’t become open-season outbound.

Not an official OpenClaw or Hermes endorsement. Not for AISDR / cold outbound.

What `assistantmail_get_usage` shows

Call assistantmail_get_usage (mailbox-scoped) when you want a clear picture before the next send fails.

Typical Free-shaped response (fields may vary slightly by MCP version):

Field	Free meaning
`plan` / `tier`	`free`
`mailboxes.used` / `mailboxes.limit`	`1` / `1`
`sends.day` (or `day`)	used vs 25/day
`sends.month` (or `month`)	`limit: null` on Free (daily cap applies)
`upgradeUrl`	In-app Upgrade deep link (Starter), tracked with `utm_campaign=mcp_limit`
`hint`	Soft copy pointing at Starter capacity + consent

Upgrade to Starter → Create Free account →

MCP itself may already return an upgradeUrl like:

https://app.assistant-mail.ai/upgrade?plan=starter&utm_source=mcp&utm_medium=error&utm_campaign=mcp_limit

Same destination; different UTM (blog click vs MCP error click). Prefer the URL the tool returned mid-incident.

Limit errors that point to Upgrade (429 / 403)

When create-mailbox or send hits a Free ceiling, MCP surfaces a structured error — often 403 (mailbox) or 429 (send/rate) — with an Upgrade hint and URL.

Mailbox limit (example shape)

{
  "error": "mailbox_limit",
  "message": "You’ve hit the Free mailbox limit (1).",
  "code": "mailbox_limit",
  "hint": "Upgrade to Starter for 1,000 emails/mo and consent invites.",
  "upgradeUrl": "https://app.assistant-mail.ai/upgrade?plan=starter&utm_source=mcp&utm_medium=error&utm_campaign=mcp_limit"
}

Send / daily usage cap

Same pattern: message names the Free 25/day (or remaining) limit, hint points at Starter, and upgradeUrl carries utm_campaign=mcp_limit. Treat 429/403 with upgradeUrl as the product’s intended next step.

Operator checklist:

Call assistantmail_get_usage — confirm day used/limit and mailbox used/limit.
If the error body includes upgradeUrl, open it (MCP-tracked).
Or use the Upgrade CTA from this post.
Still evaluating? Stay on Free — Free CTA.

Concrete limits

	Free	Starter — $9.99/mo
Mailboxes	1	3
Send volume	25 / day	1,000 / mo
Recipients	Allowlist before send	Consent invites
Upgrade	—	In-app Upgrade → Checkout

Stay on Free while one personal agent + allowlist is enough. Upgrade when you need a second/third mailbox, monthly headroom past 25/day, or consent invites.

Install / reconnect

ClawHub / OpenClaw skill: openclaw skills install @assistantmail/assistant-mail
MCP server: npx @assistantmail/assistantmail-mcp
Docs: assistant-mail.ai/docs
Set ASSISTANT_MAIL_API_KEY, list mailboxes for UUID mailboxId, then assistantmail_get_usage / assistantmail_send_email.

Upgrade or stay on Free

Primary (cap hit):

Upgrade to Starter →

Secondary (try Free):

Create Free account → Read the docs

Assistant Mail — allowlist agent email for OpenClaw & Hermes operators. Free caps are intentional; when MCP points you at Upgrade, Starter ($9.99) is the next step. Not cold outbound.