263常见退信解释
550 user not exist:收信人地址不存在
550 mailbox limit exceeded:收信人邮箱已满
550 mail size limit exceeded:发送的信件大小超过了对方的接收限制
550 sender in prision:发信人邮箱地址被临时挂起
550 ip in prision:发信方ip地址被临时挂起
520 ip and spf record not match:触犯spf规则,邮件被拒收
554 Sender address rejected Access denied:触犯同域认证规则,邮件被拒收
598 ip address in blacklist for more details:发信方服务器的ip地址在263接收服务器的黑名单中