Inbound Email API: Webhooks vs. Polling

Webhooks are usually the better fit when your application should react soon after an inbound message arrives. Polling can be simpler when delayed processing is acceptable or you need a retrieval loop you control. The choice is not just about speed: plan for retries, duplicate events, recovery after downtime, and a way to find messages your system missed.

First, separate receiving from outbound events

An inbound email API accepts or exposes messages sent to an address or domain your application handles. A provider may notify your service when a message arrives, or let your service retrieve available messages. Those are the two patterns this guide calls webhooks and polling.

Do not confuse inbound message notifications with outbound delivery webhooks. Outbound events report what happened to messages your application sent; they do not deliver incoming email content to your application. The cited inbound email API pages illustrate the category of developer-facing services, but the exact endpoints, event payloads, retry policies, and retrieval capabilities vary by provider. Verify those details in the documentation for the service you select. 1

How webhooks and polling differ

With a webhook, your service exposes an HTTP endpoint. When the provider reports an inbound message, your endpoint validates the request, records the event, and hands work to a queue or worker. The provider initiates the notification; your application still needs to retrieve or process the message data according to that provider’s API.

With polling, a scheduled worker asks the provider for messages after a known point, such as a cursor or timestamp. Your application controls when to check and how quickly to process results. Polling does not remove the need for reliable state: the worker must persist its progress and handle messages that appear between checks.

This table describes implementation tradeoffs, not a guarantee that a particular provider supports replay, cursors, or a specific retry policy. Confirm those capabilities before choosing an architecture.

A practical decision procedure

1. Set the acceptable processing delay. If the application needs to react shortly after receipt, start by evaluating webhooks. If a scheduled delay is acceptable, polling may be sufficient.
2. Inspect recovery options. Ask whether the provider retries failed notifications, how long retries continue, whether you can replay events, and whether you can list or retrieve messages after a known cursor. Do not assume “webhooks” means replay is available.
3. Choose a durable checkpoint. For polling, persist the cursor only after the retrieved batch is durably recorded. For webhooks, persist the event or message reference before acknowledging receipt. Keep enough state to reconcile after an outage.
4. Make work idempotent. Use a stable provider message or event identifier when available. Enforce uniqueness in storage and make downstream actions safe to repeat. If a stable identifier is unavailable, define a cautious fallback key and understand its collision risks.
5. Add reconciliation. A periodic retrieval or audit job can compare what your application has processed with what the provider can still return. Establish the provider’s retention and pagination behavior first; a backfill plan is only useful if the underlying data remains retrievable.

For example, suppose a support system needs to create a ticket from each received email, and a delay of several minutes is acceptable. If the provider offers reliable listing from a persisted cursor, polling can be a reasonable starting point: retrieve a page, save messages and processing state, then advance the cursor. If the workflow needs faster reaction, use a webhook to enqueue work, but retain a separate reconciliation path. In either design, a retry should not create a second ticket for the same message.

Webhook implementation: acknowledge safely

Keep the request handler small. Validate the provider’s request according to its documentation, record a durable event or message reference, and enqueue the remaining work. Avoid doing slow attachment parsing or business actions inline before responding; a timeout can lead to a retry while the original work is still running.

Define what an acknowledgement means in your system. A useful boundary is “durably accepted for processing,” not “every downstream action completed.” Track processing status separately so workers can retry failures without requiring the provider to resend the notification. See Email webhook acknowledgement and processing for a deeper treatment of that boundary.

If the provider signs notifications, verify the signature and apply the provider’s replay protections. Do not treat a valid signature alone as proof that a request is fresh. See Email webhook signature and replay protection. Keep provider-specific verification details in configuration and tests rather than assuming all providers use the same scheme.

Polling implementation: advance state carefully

Use a persisted cursor or other provider-supported checkpoint rather than relying only on the worker’s last in-memory timestamp. Fetch results in pages, record each item durably, and advance progress only when the corresponding work is safely stored. If the provider’s API uses timestamps, learn whether results can share timestamps and whether pagination is stable; otherwise, a timestamp-only checkpoint could skip or repeat items.

A small overlap between retrieval windows can help catch delayed visibility, but it also creates duplicates. Pair any overlap with idempotent processing. Set a bounded retry policy for temporary failures, alert on a cursor that stops advancing, and document how operators can restart from an earlier point. Use provider limits and documented retention windows to set polling frequency and backfill scope.

Where RepMail fits

RepMail by LetsZero is an outbound email platform, not an inbound email API described by the sources cited here. Its verified product path sends campaigns through AWS SES SMTP from a verified custom sending domain or subdomain. Do not infer from that outbound capability that RepMail receives inbound messages, provides inbound webhooks, or supports inbound polling. For a broader implementation pattern around AWS SES message formats, see AWS SES API v2: formatted vs. raw.

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