First describes the following message type: URL and file.
In general, if you choose the URL then return 404 page is 200 status (that is, return to the search engine is the normal existence of the page), and select the file is to tell the search engine did not find the page, return is 400 page content, so that the search engine to tax has a good degree of friendliness, In fact, most of us now use file format.
Recommended use of documents AH
Steps/Methods
Open IIS
Find your site, right click, select Attributes
Select the Custom Errors tab to find the 404 item, click the Edit Properties button
In the message type, select URL, and then in the URL box below, fill in the path of your 404 error file.
In the "message type" If you choose "File", in the following "file" input box, fill in your site's 404 pages on the hard drive path
And then "OK" all the way.