Unverified50% confidenceFactExact time
退信（Bounce）或不可投递报告（NDR）是SMTP协议中通知发送方投递失败的标准机制，由RFC 3464规范定义
1
Sources
50%
Confidence
Long-term
Relevance
7/6/2026
First Seen
Sources
Apple Hide My Email Security Flaw Exposed: Real Email Addresses at Risk of Leakage
hackernewshackernews7/3/2026
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.79% 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60% similarUnverifiedRFC 5321是IETF制定的SMTP标准，规定邮箱地址local-part的解释权归属于接收方邮件服务器60% 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57% similar
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