Unverified50% confidenceSolutionExact time
When an email is flagged as abusive by JEV, the send request is rejected directly at the API layer with a 400 error, and no SMTP handshake occurs.
1
Sources
50%
Confidence
Medium-term (~90 days)
Relevance
9/21/2026
First Seen
Valid until: 12/20/2026
Sources
Related Entities
Related Claims
UnverifiedIn the standard SMTP process, when an email is sent to a non-existent address, the receiving server returns a 5xx error code (such as 550 User Unknown) and the sender receives an NDR bounce notification.67% similarUnverifiedSMTP协议存在致命缺陷：任何人都可以在邮件的发件人字段填写任意地址62% similarUnverifiedDMARC记录中p=reject表示对验证失败邮件直接拒收，rua指定接收聚合报告的邮箱，还支持pct和sp参数59% similarUnverifiedHTTP status code 400 indicates a malformed request body, 401 indicates invalid or missing credentials, 403 indicates insufficient permissions, 429 indicates a rate limit has been triggered, and 5xx points to server-side issues.59% similarUnverifiedHolehe determines whether an email address is registered by exploiting behavioral differences in websites' forgot-password and registration interfaces, rather than through brute force or credential stuffing.58% similar
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