Email Events (Resend)

Synapse receives webhook events from Resend for email delivery tracking. These events update email log records, create contact activity timeline entries, and power your analytics dashboard.

Webhook Endpoint

POST https://synapse-api.pyrx.tech/v1/webhooks/resend

This endpoint is configured automatically when you set up Resend integration in your workspace settings.

Note

You do not need to configure this webhook yourself. Synapse manages the Resend webhook subscription. This documentation is for understanding how email tracking works.

Supported Events

Resend Event	Synapse Event Name	Description	Action
`email.sent`	`email_sent`	Email accepted by Resend for delivery	Logged only (already marked as sent during send)
`email.delivered`	`email_delivered`	Email accepted by recipient's mail server	`email_logs.status` set to `delivered`, `delivered_at` set
`email.delivery_delayed`	`email_delivery_delayed`	Temporary delivery delay (soft bounce, server busy)	Delay reason logged; status unchanged (Resend retries automatically)
`email.opened`	`email_opened`	Recipient opened the email (pixel tracking)	`email_logs.first_opened_at` set on first open
`email.clicked`	`email_clicked`	Recipient clicked a link in the email	`email_logs.first_clicked_at` set on first click
`email.bounced`	`email_bounced`	Email permanently rejected (hard bounce)	`email_logs.status` set to `bounced`, contact auto-unsubscribed
`email.complained`	`email_spam_reported`	Recipient marked the email as spam	`email_logs.status` set to `complained`, contact auto-unsubscribed
`email.failed`	`email_failed`	Send failure on Resend's side	`email_logs.status` set to `failed`, error message captured
`email.suppressed`	`email_suppressed`	Email blocked by Resend suppression list	`email_logs.status` set to `suppressed`, reason captured

Webhook Payload

Resend sends individual event objects (not batches). Each event has this structure:

json

{

"type": "email.delivered",

"created_at": "2026-04-01T10:30:00.000Z",

"data": {

"email_id": "re_abc123def456",

"from": "[email protected]",

"to": ["[email protected]"],

"subject": "Your claim has been submitted",

"headers": [

{"name": "X-Email-Log-Id", "value": "8f14e45f-ceea-467f-a83c-01a01ba3c5db"}

]

}

Synapse matches events to email log records using the X-Email-Log-Id custom header, which is injected into every outgoing email. If the header is missing, Synapse falls back to matching by data.email_id against the provider_message_id field.

Signature Verification

Resend uses Svix for webhook signing. Verification uses three headers:

Header	Description
`svix-id`	Unique message identifier
`svix-timestamp`	Timestamp used in signature generation
`svix-signature`	HMAC signature of the payload

See Signature Verification for implementation details and code examples.

Event Processing

Delivered

When an email is delivered, Synapse updates the log record:

email_logs.status = 'delivered'

email_logs.delivered_at = event.created_at

Opened

First-open tracking (subsequent opens are counted but do not update the timestamp):

email_logs.first_opened_at = event.created_at (only if NULL)

email_logs.status = 'opened'

Warning

Open tracking relies on a 1x1 pixel image. Email clients that block images (Apple Mail Privacy, Outlook) may not register opens. Open rates should be treated as a lower-bound estimate.

Clicked

First-click tracking:

email_logs.first_clicked_at = event.created_at (only if NULL)

email_logs.status = 'clicked'

Bounced (Hard Bounce)

Hard bounces indicate a permanent delivery failure:

email_logs.status = 'bounced'

email_logs.bounced_at = event.created_at

email_logs.error_message = data.bounce.message

contact.subscription_status = 'unsubscribed' (automatic)

Warning

Contacts that bounce are automatically unsubscribed to protect your sender reputation. Do not re-subscribe contacts who have bounced -- verify the email address first.

Complained (Spam Report)

When a recipient marks your email as spam:

email_logs.status = 'complained'

email_logs.error_message = 'Spam complaint'

contact.subscription_status = 'unsubscribed' (automatic)

Contacts who file spam complaints are automatically unsubscribed and will not receive any further emails. This is enforced at the delivery pipeline level.

Delivery Delayed

Resend fires this event when delivery is temporarily delayed (soft bounce, recipient server busy). Synapse logs the delay reason but does not change the email status -- Resend retries delivery automatically.

email_logs.error_message = 'Delivery delayed: <reason>'

email_logs.status = (unchanged -- remains 'sent' or 'queued')

Failed

A send failure on Resend's side (infrastructure error, rejected by Resend):

email_logs.status = 'failed'

email_logs.error_message = data.error.message

Suppressed (Provider)

The email was blocked because the recipient is on Resend's suppression list (previous hard bounce or spam complaint on Resend's side):

email_logs.status = 'suppressed'

email_logs.error_message = data.suppression.message

Note

Provider-level suppression (from Resend's suppression list) is different from NLT suppression (from the required modifier). Both result in a suppressed status, but the error message indicates the cause.

Activity Timeline

For each recognized event, Synapse creates an Event record on the contact's activity timeline. Timeline events include:

email_log_id -- the internal email log record
email_subject -- the rendered email subject
to -- the recipient address
email_provider -- always "resend" for Resend events
resend_email_id -- the Resend email ID (when available)
url -- the clicked link URL (for click events)

curl "https://synapse-api.pyrx.tech/v1/email-logs?status=bounced&date_from=2026-04-01" \

-H "Authorization: Bearer <jwt>"

Contact Status Lifecycle

subscribed ──(hard bounce)──> unsubscribed

subscribed ──(spam report)──> unsubscribed

subscribed ──(user opt-out)──> unsubscribed

Status	Can Receive Email	Triggered By
`subscribed`	Yes	Default state, manual re-subscribe
`unsubscribed`	No	Hard bounce, spam complaint, user opt-out