184.108.40.206.3 HTTP Error 503
One of the causes of HTTP error 503 is that more users than are allowed by the server's request queue limit have sent requests to a single server.
The error returned by the server resembles the following.
OPTIONS /Microsoft-Server-ActiveSync Content-Type: application/vnd.ms-sync.wbxml MS-ASProtocolVersion: 14.0 HTTP/1.1 503 Service Unavailable Connection: close Date: Mon, 02 Mar 2009 23:51:51 GMT Server: Microsoft-IIS/7.0 X-Powered-By: ASP.NET Content-Type: text/html
If a Retry-After header ([RFC2616]) is present in the response, the client SHOULD<5> retry the request after waiting the number of seconds indicated by the Retry-After header. Any such value represents an estimate of when the server is expected to be able to process the request.
If a Retry-Header is not present in the response, the client can retry the request after waiting a few seconds. The time to wait between continuous requests that result in HTTP error 503 responses can be increased exponentially to a predetermined maximum.
For more details about ASP.NET performance monitoring properties, see [MSDN-APM].