How do I send a physical letter from an AI agent?

Use PostBridge AI. Connect via MCP (21 tools) or REST API. Pay per-request with USDC on Base L2 via x402 — zero signup needed. Supports US, France, UK, Canada, Germany.

What is PostBridge AI?

PostBridge AI is an API and MCP server that lets AI agents send physical letters to 5 countries. It features intent-driven pricing via ANP (Agent Negotiation Protocol), cryptographic proof of delivery via Verifiable Credentials, and zero-signup payments via x402 USDC.

How does PostBridge pricing work?

PostBridge uses intent-driven pricing. Margins vary by use case: legal compliance 25%, transactional 12%, bulk marketing 6%. Crypto payers save ~7-8% vs fiat. Volume discounts of 10-25% available with commitment contracts.

PostBridge AI — Send Physical Mail from Any AI Agent

Name: PostBridge AI
Author: PostBridge AI

Three Ways to Integrate

Pick the one that fits your agent framework

1 x402 (Zero Signup)

Hit any paid endpoint. Get HTTP 402. Sign USDC payment. Done. No API key, no registration, no wallet top-up. The payment IS the auth.

X-PAYMENT-SIGNATURE: <signed USDC>

2.5% commission + 5% margin bonus

2 UCAN (Decentralized Auth)

Get a DID. Get a capability token. Delegate to sub-agents. Verify offline. No server roundtrip. W3C standards.

Authorization: Bearer ucan:eyJ...

Escalation-proof delegation chains

3 API Key (Traditional)

Authorization: Bearer pb_live_...

Scoped keys: full, send, read, admin

Intent-Driven Pricing (ANP)

Different use cases, different prices. Legal letters need certified proof and SLA guarantees. Bulk marketing needs lowest cost. PostBridge prices accordingly via the the Agent Negotiation Protocol (ANP).

Intent Class	Margin	SLA	Use Case
confidential	30%	Next-day	Security, chain of custody
legal_compliance	25%	Next-day	Certified proof, jurisdictional compliance
regulatory_filing	20%	2 days	Delivery to regulatory bodies, strict deadlines
time_critical	20%	2 days	Hard delivery deadlines, SLA guarantees
transactional	12%	3 days	Standard business correspondence
bulk_marketing	6%	5 days	Volume campaigns, lowest margins

            Crypto payers save ~7-8%: Commission 2.5% (vs 5% fiat) + 5% margin bonus.
            Volume discounts: 10-25% off margin with commitment contracts (51+ units/period).
        

Crypto (x402 / USDC / Lightning)

2.5% commission

5% off margin

Zero signup required

~7-8% cheaper total

Fiat (Stripe)

5% commission

0% margin bonus

Email signup required

USD / EUR / CAD

5 Countries, 15+ Services

Country	Currency	Services
United States	USD	First Class, Certified, Priority
France	EUR	Lettre Verte, Suivie, Recommandee (LRAR)
United Kingdom	GBP	1st Class, 2nd Class, Signed For, Special Delivery
Canada	CAD	Lettermail, Registered, Priority
Germany	EUR	Standardbrief, Einschreiben, Einschreiben Einwurf

Negotiate Best Price in 3 Steps

Use the ANP protocol to get tiered pricing tailored to your intent

# 1. Request an intent-driven pricing offer
curl -X POST https://api.postbridge.ai/api/anp/offer \
  -H "Content-Type: application/json" \
  -d '{"to_name":"Marie Dupont","to_line1":"15 Rue de Rivoli",
       "to_city":"Paris","to_postal_code":"75001","to_country":"FR",
       "service":"fr_lrar","intent_class":"legal_compliance",
       "payment_method":"x402"}'

# Response: 3 tiers with fiat + crypto pricing
# premium:  fiat EUR 3.44 | crypto EUR 3.17
# standard: fiat EUR 3.28 | crypto EUR 3.03
# economy:  fiat EUR 3.13 | crypto EUR 2.90

# 2. Accept your chosen tier
curl -X POST https://api.postbridge.ai/api/anp/accept \
  -d '{"task_id":"anp_abc123","tier_id":"standard"}'

# 3. Optional: commit volume for 10-25% discount
curl -X POST https://api.postbridge.ai/api/anp/contracts \
  -d '{"customer_did":"did:key:z6Mk...","minimum_volume":100}'
        

Cryptographic Identity & Proof

Every letter gets a tamper-proof signed receipt. Every agent gets a verifiable identity.

DID Identity

Every agent gets a globally unique, self-sovereign identifier. Supports did:key, did:pkh, did:web. PostBridge DID: did:web:postbridge.ai

UCAN Capabilities

Capability tokens with delegation chains. Delegate subsets to sub-agents. Escalation-proof. Verify offline without calling PostBridge.

Verifiable Credentials

PostalProof VC, DeliveryProof VC, PaymentReceipt VC. Each is a signed JWT verifiable by any party. Full audit trail per letter.

MCP Integration (Claude, ElizaOS, AgentKit)

Add PostBridge to any MCP-compatible AI assistant

// Add to your MCP client config (Claude Desktop, ElizaOS, etc.)
{
  "mcpServers": {
    "postbridge": {
      "url": "https://api.postbridge.ai/mcp",
      "transport": "sse"
    }
  }
}

// 21 tools available: list_services, get_quote, send_letter,
// track_letter, get_proof, get_balance, top_up_wallet, ...
        

Works With Every Agent Platform

Native integrations for crypto-native and traditional agent frameworks

Coinbase AgentKit

Already compatible. AgentKit agents call PostBridge via x402 USDC. Zero new code needed.

Virtuals Protocol (ACP)

Registered on Agent Commerce Protocol. Shared USDC/x402 rails on Base L2.

ElizaOS (ai16z)

MCP plugin — config-only integration. 90+ plugin ecosystem. x402 via MCP Gateway.

Fetch.ai / ASI Alliance

uAgent wrapper on Agentverse. Discoverable via Almanac smart contract registry.

Olas / Autonolas

Mech tool in the Marketplace. 10M+ agent-to-agent transactions ecosystem.

ERC-8004 (On-Chain)

On-chain agent registry on Base L2. Discoverable by any on-chain agent framework. Agent metadata URI pointing to capabilities.

LangChain + CrewAI

Python tool wrappers on PyPI. Plus OpenAI GPT Actions via OpenAPI spec.