How to avoid duplicate email sends with Hail MCP

Description and use

An automation recipe that uses idempotency keys and external state tracking to prevent duplicate email sends when connections drop during AI agent retries.

Problem

An AI agent sends an email, the service accepts it, but the connection drops before the agent receives an answer, leading to possible duplicate emails on retry.

Outcome

Implementing idempotency keys and external state tracking prevents duplicate email sends when connections drop during AI agent retries.

Workflow

• Generate a unique idempotency key before the first send
• Pass the key and message details to Hail’s send_email tool
• Store campaign, lead, message, key, state, Hail email ID, and last attempt time in a database
• If a timeout occurs, mark the operation as unknown and do not requeue
• Before retrying, check Hail’s get_email or saved response for the key
• If the result is still unknown, pause for review instead of creating a new key
• Resume batch processing one message at a time, claiming operations atomically
• Test the lost-response scenario by simulating accept, drop, retry, and verify single acceptance

Evidence

An AI agent sends an email, then the service accepts it, but the connection drops before the agent gets an answer.

Source

Hail’s send_email tool accepts an idempotency_key. If you leave it out, the tool creates a fresh UUID for that invocation.

Source

If the connection drops without a result, mark the operation as unknown. Do not quietly return it to the unsent list.

Source