X_MAIL_EVENT_UNVERIFIED
Means
a delivery notification is not signed by its provider
Typical cause
no signature, a bad signature, a stale timestamp, a topic not in topicArns, a certificate URL off sns.<region>.amazonaws.com, or a SignatureVersion other than 1 or 2 (meta.reason says which)
Fix
sesEventReceiver({ topicArns: ['<your topic arn>'] }) — or resendEventReceiver({ secret }) with the endpoint's whsec_ secret