请问系统退信？

simplelife

我用163的邮箱在outlook express 发送邮件到 tongxue@sina.com，信到达不到对方，系统退信。

下面是内容。

This message is generated by COREMAIL email system. I'm sorry to have to inform you that the message returned The message to tongxue@sian.com is bounced because : SMTP error, RCPT T 550 5.7.1 <tongxue@sian.com>... Relaying denied. IP name lookup failed [202.108.44.205] 你发送到tongxue@sian.com的邮件由于以下原因被退回 : SMTP error, RCPT T 550 5.7.1 <tongxue@sian.com>... Relaying denied. IP name lookup failed [202.108.44.205]

请问这是为什么呀？

DC.Direct

我也老收到，而且我根本从未发过，可能是最近病毒泛滥的结果。