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An email API workflow has three distinct stages: publish the provider’s DNS records to authenticate your sending domain, submit messages through the API, then use webhooks and searchable logs to track what happened. A successful API response confirms submission—not inbox delivery—and a “delivered” event usually means the recipient’s mail server accepted the message, not that it reached the inbox.
What does a verified sending domain mean?
A verified sending domain is one for which the email provider has recognized the DNS records it requires. The domain owner publishes those records at the DNS host; the email API is a separate service that sends messages. Use the exact values shown for your provider and account rather than copying a record from another service or an old tutorial.
Three authentication mechanisms have distinct roles:
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- DKIM lets recipient systems check a cryptographic signature against a public key published in DNS.
- DMARC specifies policy for messages that appear to use a domain but fail authentication checks.
These mechanisms work together, but the records and alignment behavior depend on the provider and configuration. Twilio SendGrid’s setup documentation describes domain authentication as part of onboarding and discusses SPF and DKIM; its authentication guide explains SPF, DKIM, and DMARC (domain authentication setup; authentication overview).
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Some DNS records serve related but different purposes. SendGrid documents link branding as a separate setup: CNAME records make tracked links appear to use the customer’s domain while activity is routed back to SendGrid. Its onboarding documentation says reverse DNS is required only for accounts using dedicated IP addresses (SendGrid domain setup).
Why a “verified” flag may not prove current DNS health
Provider status fields can have provider-specific meanings. Postmark’s Domains API says its DKIMVerified field records whether DKIM has ever been verified and remains true even if the DNS record is later removed. The API also exposes current DKIM host and value fields, plus pending values for rotation. Its SPF verification fields and endpoint are marked deprecated. Check the provider’s current setup guidance and the DNS record itself; do not infer present health from a historical boolean alone (Postmark Domains API).
How does an API send request lead to a delivery event?
The API send and later delivery status answer different questions. A typical sequence is:
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- Submit a message. Your application authenticates to the email service and sends the sender, recipient, subject, and content to its API.
- Save the response identifiers. Keep the provider’s message ID and submission timestamp with your own application record.
- Receive later events. A webhook can report a later lifecycle event, while searchable message logs let you investigate or reconcile activity.
For example, Postmark’s Email API requires a registered, confirmed sender signature for the From address. It accepts text or HTML content and supports tags, metadata, tracking options, attachments, and a message stream. Its response includes MessageID and SubmittedAt. Those fields document successful API submission; they do not prove the destination accepted the message (Postmark Email API).
Preserve the message ID as a correlation key. Tags or metadata can also connect provider activity to an application user, transaction, or workflow. Postmark exposes tags and metadata when sending and in message details; other providers use their own field names (Email API; Messages API).
What does a delivered email webhook mean?
Postmark defines delivery this way: “Delivery means the receiving server accepted your message, but it doesn’t guarantee it reached the recipient’s inbox.” A delivery event is therefore evidence of acceptance by the receiving server—not proof of inbox placement or that a person saw the message (Postmark Delivery webhook).
Keep these stages separate when interpreting status:
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- Provider processing: The provider handles the message after submission.
- Receiving-server acceptance: The destination server accepted it; this is what Postmark’s delivery event means.
- Bounce or complaint: A later event may report rejection or a recipient complaint.
- Open or click observation: Tracking can record an image load or link interaction, but neither is a definitive measure of human attention.
Events can be recipient-specific. Postmark says a message addressed to several recipients may generate separate delivery events, so correlate and process events at the recipient level when the event payload provides that detail (Delivery webhook). Open and link tracking are configurable options in Postmark’s send API (Email API).
How should an application handle email webhooks?
A webhook is an HTTP POST from the provider to a public endpoint in your application when a selected event occurs. Treat that endpoint as a production API: validate the payload, correlate it to a message, handle duplicates safely, and acknowledge events only after processing them or safely queuing the work.
- Expose and protect an HTTPS endpoint. Apply the authentication and network controls supported by your provider.
- Validate the event shape. Reject malformed or unexpected payloads without triggering application side effects.
- Make processing idempotent. Providers may retry delivery, so repeated events should not cause repeated actions such as issuing multiple refunds or sending duplicate notifications.
- Persist the useful event data. Store enough to diagnose and reconcile lifecycle changes, while minimizing message content and recipient data.
- Return success after handling or safely queuing the event. Monitor endpoint health and the provider’s status for each enabled event type.
Webhook security and retry contracts are provider-specific. Postmark says its outbound webhooks are not signed and recommends protections such as HTTP Basic Authentication and IP allowlisting. Its documentation says it tests enabled outbound event types and checks for a 200 response during verification. If an event type persistently fails later, Postmark can mark it unverified and pause delivery until the endpoint is repaired and verified again. Do not assume another provider uses the same security scheme or failure behavior (Postmark webhook overview).
How do I find an email by message ID?
Start with the message ID returned by the send API, then search provider activity or request the message’s details. Postmark’s Messages API supports outbound searches filtered by recipient, sender, tag, status, dates, subject, stream, and metadata, and provides message details by ID. SendGrid documents an Email Logs API for structured event-level history with filtering and lookup by message ID (Postmark Messages API; SendGrid Email Logs API).
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If you do not have a message ID, search using the narrowest available combination of recipient, time range, status, and other known fields. Once you find a candidate, inspect its event sequence and recipient-specific status rather than treating the original API response as the final outcome.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How long do email API logs stay available?
Retention and access differ by provider and feature. The figures below are documented in provider documentation accessed in 2026; they are product limits, not industry standards.
| Provider record | Documented history | Access notes |
|---|---|---|
| Postmark Messages API | 45 days by default; configurable from 7 to 365 days | Search and message details are available through the API. Source |
| Twilio SendGrid Email Logs API | 30 days of event history; retention cannot be extended | Structured event-level history with filters and message-ID lookup. Source |
| Twilio SendGrid Email Activity Feed | Up to 30 days with the history add-on | Provides event sequence, search and filtering, and CSV download. Documentation says activity data is stored in the United States; confirm current access and account requirements. Source |
Check the current feature availability, add-on requirements, retention, and regional handling for the account you use. If you need history longer than the provider retains it, persist relevant webhook events or export records to your own logging or analytics system. Apply your organization’s data-access and retention rules, and avoid storing message content or recipient details that are not needed for diagnosis.
What should you check when choosing an email API?
Compare the operational behavior that affects your sending workflow, not just whether an API can submit a message:
- Domain setup: Required authentication records, custom Return-Path or link branding options, and whether dedicated IPs add DNS requirements.
- Webhook behavior: Event coverage, verification requirements, retry behavior, endpoint security options, and how failures affect event delivery.
- Investigation tools: Search filters, message-ID lookup, correlation fields, API access, and UI or export options.
- History limits: Retention period, plan or add-on requirements, and regional data handling.
- Tracking controls: Whether opens and clicks must be enabled and what those observations can—and cannot—tell you.
These details vary by provider, account, and configuration. Verify them in the current documentation and account dashboard before relying on a specific status field, security mechanism, or retention period.
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