404 pages are used to redirect users of a website when they reach a page that has been deleted, renamed or moved. A 404 page can prevent your traffic from leaving your web site by providing them directions to the information they seek. Directions differ depending on whether you are on a UNIX sever or a Windows server.
Regardless of your web hosting server model:
Create a normal HTML page with 404 information. This information usually includes an index of all the site pages or a link to the sitemap. A request for the user to tell you about broken links might help you make local corrections if needed.
Create a text file (use NotePad or another plain text editor) and name it ".htaccess" (without the quotes, but do notices the period in front of htaccess) and add the following line (the URL provided should point to your error page):
ErrorDocument 404 http://www.yourdomain.com/yourerrorfile.html
This ErrorDocument 404 command with URL needs to be listed on one line in your .htaccess file.
Upload both your 404.html page and your .htaccess page. Assuming your host allows parsing of non-shtml files, that should be it. If you web host does not allow parsing of non-shtml files, you will have to name your 404 document 404.shtml.
Warning: you will need access to the server's IIS or you will need to ask your web host to do this for you.
Open the Internet Service Manager and right click on the web site for which you want to set the custom 404 Error page.
Choose "Properties" and then the "Custom Errors" tab. Scroll down until you get to the 404 in the HTTP Error column. Under Contents in the right column you will see that it has a filename associated with the 404 status listed.
Highlight this line, click edit. Browse to the 404.html or 404.htm document that you have created. Click OK twice to leave this dialog box and IIS and you are done!