这句话是什么意思"The following message to was undeliverable.”The following message to was undeliverable.The reason for the problem:5.1.0 - Unknown address error 550-',\xca\xd5\xd0\xc5\xc8\xcb\xce\xb4\xd6\xaa\xa1\xa3'电子邮件发送过去

这句话是什么意思"The following message to was undeliverable.”
The following message to was undeliverable.
The reason for the problem:
5.1.0 - Unknown address error 550-',\xca\xd5\xd0\xc5\xc8\xcb\xce\xb4\xd6\xaa\xa1\xa3'
电子邮件发送过去退回来的退信信息

服务器返回的东西,服务器逻辑决定的