Use Certified Mail Sender with your AI assistant
Your AI assistant can write a Certified Mail letter for you and get it ready to send. You check the letter and pay; nothing is mailed before that. This works with assistants that support MCP, such as Claude, and with any assistant that can call a web API.
Connect with MCP
It uses Streamable HTTP and needs no sign-in. Copy this MCP server URL:
https://certifiedmailsender.com/mcpClaude on the web, desktop or phone
- Open Customize, then Connectors, and choose + Add, then Add custom connector.
- Name it Certified Mail Sender and paste the MCP server URL above.
- For authentication, choose No sign in, then Add.
On Team and Enterprise plans an owner adds it under Organization settings, then Connectors. See Claude’s guide to custom connectors.
Claude Code
claude mcp add --transport http certifiedmailsender https://certifiedmailsender.com/mcpAdd --scope user to use it in every project. See Claude Code’s MCP guide.
Codex
Add or update this block in ~/.codex/config.toml (or config.toml in your CODEX_HOME):
[mcp_servers.certifiedmailsender]
url = "https://certifiedmailsender.com/mcp"
omit_tools_from = ["deferred"]Without omit_tools_from, Codex hides MCP tools until the agent goes looking for them, and agents often don't. See OpenAI’s Codex MCP guide.
Ask: “Use Certified Mail Sender to…” Some assistants keep tools out of sight until a request points at them.
Other MCP clients
Add the MCP server URL above as a remote (Streamable HTTP) server. An API key is optional: send it as Authorization: Bearer <key> to list your letters or use auto-send. Create one from your account.
What your assistant can do
| Tool | What it does |
|---|---|
quote_letter | Quote a certified letter. |
create_letter | Create a certified letter draft. |
get_letter | Get a letter's status. |
list_letters | List letters. |
send_letter_now | Send a paid letter now. |
cancel_letter | Cancel a letter. |
How approval works
When your assistant creates a letter, it gets an approval_url: a private page for you. Open it yourself to see the exact letter as it will print, both addresses and the price, confirm you may send it, and pay by card. Your assistant never pays, and nothing is mailed until you do. The one exception is an API key you set to auto-send from a prepaid balance.
Your cancellation window
After payment, letters wait 30 minutes before going to the printer, including letters paid from a balance or by auto-send. You can cancel for a full refund until submission. The letter page shows the deadline. Screening runs during the hold, and a letter held for review stays cancellable while it waits.
In a hurry? Choose Send it now on the paid letter page, or ask your assistant to call send_letter_now. It can also set send_now to true when creating the draft at your request. This skips the hold, never approval, payment or screening. After skipping, there is no guaranteed cancellation period.
After cancellation, the letter page and your assistant can show the refund amount and where it went. Card refunds go back to the card you paid with; balance payments go back to your prepaid balance. A card refund usually shows on your statement within 5 to 10 business days; your bank decides exactly when.
Keep the letter link private
The letter_url (and the approval_url) carries a private token. Treat it like a password: anyone with the complete link can read your letter and its tracking. Until it goes to our printing partner, they can also pay, cancel or send it. Your assistant uses it with get_letter to follow the letter, and we email it to you when you pay.
HTTP API
The OpenAPI document describes the same flow: POST /v1/quotes for a price, POST /v1/letters with an Idempotency-Key header for a draft and its approval_url, then GET /v1/letters/{id} to follow it. No sign-up is needed for a first letter. Test mode and test keys never mail anything.
Assistants without tools
An assistant that can’t call tools can give you a link that fills in our form. Put the fields after this prefix, encoded like URL query parameters:
https://certifiedmailsender.com/send#- Recipient:
to_name,to_company,to_line1,to_line2,to_city,to_state,to_zip - Return address:
from_name,from_company,from_line1,from_line2,from_city,from_state,from_zip service:certifiedorcertified_err(with electronic Return Receipt)text: the letter, from the greeting on. We print both addresses and the date.
Example:
The part after # stays in your browser and never reaches our server. You check every field and send it yourself; the link never sends anything on its own.
For assistants reading this page
The short guide:
The full guide has every tool’s inputs, outputs and errors, the API flow and our answers to common questions:
See a sample or get help
See a fictional sample letter and its printed tracking record. For sending, payment and account questions, read the help page.