[退信] 垃圾邮件退信：Content reject/Spam denied

[退信] 发信数超限制：sending quota exceeded

[退信] 网络异常：rcpt handle timeout

[退信] 邮件过大：exceeded mailsize limit

[退信] 域名不存在：DNS query error

[退信] 收件人不存在：user not exist

[退信] 收件容量满：Quota exceeded