请求方法（GET、POST、HEAD等）对指定的资源不适用
请求资源的MIME类型和客户在Accpet头中所指定的不兼容
在服务器许可的等待时间内，客户一直没有发出任何请求
在请求头Expect中指定的预期内容无法满足服务器
origin server requires the request to be conditional
user has sent too many requests in a given amount of time
server is unwilling to process the request
server returns no information and closes the connection
request should be retried after performing action
Windows Parental Controls blocking access to webpage
the server cannot reach the client's mailbox
connection closed by client while HTTP server is processing