1. 核查错误代码：
退信错误代码为：
553 can't verify FROM domain in DNS
553 zeng.pionmi.com does not exist
remote server said: 550-Verification failed for
550-It appears that the DNS operator for bpeg.cn
550-has installed an invalid MX record with an IP address
550-instead of a domain name on the right hand side.
550 Sender verify failed
2. 原因：
邮件服务器为了防垃圾邮件的需要，接收邮件时进行对发信人的email地址进行DNS反向查询，对于公网存在正确DNS解析的发件人的邮件放行，而对于DNS反向解析不正确的地址予以拦截。
3. 处理方法：
请发件人联系邮箱服务商处理。
