Last reviewed 2026-09-05Skill version 0.1.0Community
Prove that Resend handed the email to its sending infrastructure. The sent level proves the email.sent event of this email. It does not prove that the recipient mail server accepted the message. This level needs the email.sent webhook.
idempotency_key through Idempotency-Key, retry is safe
How does the evidence correlate with this operation?
Strategy
Assurance
Keys
Required
resource_id
strong
email_id from $action.result.id
yes
idempotency_key
strong
idempotency_key from $operation.id
no
fingerprint
weak
to from $input.to; subject from $input.subject
no
Which evidence does the contract require?
Minimum evidence level E2. An independent channel is required. Minimum channels: 1.
Channel
Level
Independence
Verifier
Description
email_readback
E2
provider readback
http
Read the email record. The http verifier returns the parsed Email object, so a condition path is $observed.email_readback.last_event.
sent_events_by_intent
E3
provider event
webhook
The email.sent events for the same recipient and subject since the operation started. A count above one shows a second send. The webhook verifier returns {events, count, latest, earliest, types, duplicates_dropped}, so a condition reads the count.
sent_events
E3
provider event
webhook
The email.sent events of this email. The resource id is the data.email_id of the payload. The webhook verifier returns {events, count, latest, earliest, types, duplicates_dropped}, so a condition reads the count.
Which conditions must all hold for VERIFIED?
Condition
Meaning
Path
Operator
Expected
Evidence
record_created_in_window
The provider created the email record after the operation started.
$observed.email_readback.created_at
time_after
$operation.created_at
email_readback
sent_event_present
At least one email.sent event of this email arrived.
$observed.sent_events.count
gte
1
sent_events
Which conditions give CONTRADICTED?
Condition
Class
Reason
Path
Operator
Expected
wrong_recipient
wrong subject
The message went to a different recipient.
$observed.email_readback.to
ne
$input.to
record_predates_operation
pre existing state
The provider record is older than the operation. It proves nothing.
$observed.email_readback.created_at
time_before
$operation.created_at
more_than_one_recipient
partial completion
The record lists more than one recipient. This contract proves the outcome for one recipient. Use one operation per recipient.
$observed.email_readback.to
array_length
{"min":2}
duplicate_email_present
duplicate side effect
Resend sent more than one email for this recipient and subject since the operation started. Do not retry.
$observed.sent_events_by_intent.count
gt
1
Which observed states map to a verdict before completion?
Rule
Match
Verdict
Reason
terminal_failure
$observed.email_readback.last_event in ["failed","suppressed"]
FAILED
The provider reports that the message failed, bounced, or was suppressed.
still_transitional
$observed.email_readback.last_event in ["queued","scheduled"]
PENDING
The message is on the way. The runtime observes again later.
canceled
$observed.email_readback.last_event eq "canceled"
CONTRADICTED
The schedule of the message was canceled. The provider will not send it.
Provely