Prevent unwanted emails with an enforced approval gate; prevent duplicates with durable per-message send records and careful handling of uncertain outcomes. These solve different problems: approval decides whether an agent may send, while send-state tracking helps determine whether the same logical message was already submitted. Neither rate limits nor a successful-looking API response guarantees exactly-once delivery.
Why an AI email agent can send the same message twice
A duplicate often happens when an agent or worker retries a send after a timeout, connection loss, or other ambiguous result. The first request may have reached the email provider even if the application did not receive a clear response. If the application submits again without checking, the recipient may get two copies.
Provider responses need careful interpretation. Google says, “You can’t assume that a 200 response means the email was successfully sent” in its Gmail API error guidance. Microsoft Graph’s sendMail documentation says a 202 Accepted response means the request was accepted, not that processing has completed. An API response is therefore not always proof of final delivery.
The reviewed Gmail and Graph documentation does not promise a general idempotency key for these send operations. Build duplicate protection into the application rather than assuming a provider will collapse repeated requests into one email.
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Separate permission to send from whether a send already happened
Use two independent controls. An approval gate prevents a message the agent should not send; a durable send record helps prevent a second submission of a message that is already in progress or may have been sent. A single “safe to send” check cannot reliably answer both questions.
- Permission: require a human approval status or another explicit policy before the application calls the send operation. Restrict recipient types or domains and cap messages per run when those rules suit the workflow.
- Duplicate protection: assign each logical email a stable application-generated action ID and atomically check its persistent state at the send boundary. Repeated tool calls and concurrent workers must not both proceed unchecked.
At approval time, show the recipient list, subject, body, and attachments. Bind approval to the exact reviewed message: if its recipients or content change, require approval again. These are application-level safeguards, not controls that Gmail or Graph automatically supplies.
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Record each logical send and use an explicit state machine
Store enough information to distinguish a new message from a retry of an existing one. A useful record includes the action ID, agent run ID, recipient set, content version or hash, approval status, provider message or draft ID when available, submission time, response code, retry reason, and final observed status.
Keep state transitions explicit. One practical sequence is drafted → awaiting_approval → approved → submitting → accepted/unknown → reconciled_sent, with a separate failed outcome when failure is known. The exact labels are an implementation choice; the important point is that an ambiguous result stays distinguishable from a confirmed failure.
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Enforce the state transition atomically where the side-effecting send call occurs. A database uniqueness constraint or equivalent transaction can prevent two workers from claiming the same action at once. If a request times out after submission, mark the result unknown rather than automatically returning it to a sendable state.
What to do after a timeout or unclear response
- Stop automatic resubmission. Treat a timeout or connection loss after submission as potentially accepted by the provider.
- Check the application record. Review the action ID, submission attempt, stored response, and current state. Confirm that another worker or tool call has not already advanced the same action.
- Reconcile against the provider mailbox or available delivery state. Look for evidence that the message was created or sent, using the provider identifiers and recipient details your application retained.
- Resolve uncertainty conservatively. If available evidence cannot establish whether it was sent, hold the item for operator review rather than blindly resending.
- Retry only when failure is clearly pre-submission or otherwise established. Use bounded backoff and follow provider retry instructions and quotas. Do not hammer a
429 Too Many Requestsresponse in a tight loop.
This is a reconciliation strategy, not a provider-guaranteed exactly-once mechanism. The API documentation’s uncertainty is precisely why an application should preserve state and avoid treating every missing response as proof that nothing happened.
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Use drafts to create a review point where supported
Microsoft Graph supports separate draft creation and sending operations. An application can create a message with Create message, present the draft for review, and later send it with Send draft. This separation gives the workflow a natural checkpoint, but the API sequence does not itself require a person to approve the draft; the application must enforce that rule.
Handle rate limits without mistaking them for deduplication
Rate limits control sending volume; they do not identify repeated logical messages. Google’s Gmail API guidance covers quota errors, including 429 responses, daily sending limits, and per-user concurrent request limits. Google also notes that a delay can occur before quota errors appear. Consult the current Gmail API usage limits for the relevant Google Cloud project: applicability depends on project history, and the page states quota changes taking effect May 1, 2026 for applicable projects.
Microsoft Graph’s sendMail documentation notes that delivery is subject to Exchange Online limitations and throttling. Respect provider throttling and retry guidance, but keep the per-message state check as a separate control.
Google’s Email sender guidelines recommend a consistent sending rate and monitoring. For senders sending more than 5,000 messages a day to Gmail accounts, Google requires SPF, DKIM, and DMARC configuration; it recommends keeping the spam rate shown in Postmaster Tools below 0.30%. These are sender reputation and deliverability considerations, not duplicate-send safeguards.
Quick Recap
Make failures visible and test before live sending
- Log each logical action ID alongside the agent run, recipient set, timestamps, approval record, provider response, and retry reason.
- Provide an operator pause or kill switch for the sending workflow so an emerging duplicate pattern can be stopped quickly.
- Before enabling live sending, use a test mailbox or controlled recipients. Simulate timeouts and duplicate tool invocations, then verify that persistent state prevents a second send.
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