IIS status code editing under HTTP
1XX – Information prompt
These status codes represent temporary responses. The client should be prepared to receive one or more 1XX responses before receiving the general response.
100 – Go ahead.
101 – Switch protocol.
2 xx – success
This type of status code indicates that the server has successfully accepted the client request.
200 – Ok. The client request has been successful.
201 – Created.
202 – Accepted.
203 – Non-authoritative information.
204 – No content.
205 – Reset content.
206 – Part content.
3XX – Redirection
The client browser must do more to implement the request. For example, a browser might have to request a different page on the server or repeat the request through a proxy server.
301 – The object has been permanently removed, that is, permanently redirected.
302 – The object has been temporarily moved.
304 – Not modified.
307 – Temporary redirection.
4XX – Client error
An error has occurred and there seems to be a problem with the client. For example, if the client requests a page that does not exist, the client does not provide valid authentication information. 400 – Wrong request.
401 – Access denied. IIS defines a number of different 401 errors that point to a more specific reason for the error. These specific error codes are displayed in the browser but not in the IIS log:
401.1 – Login failed.
401.2 – Server configuration causes logon failure.
401.3 – not authorized due to ACL restrictions on resources.
401.4 – Filter authorization failed.
401.5 – ISAPICGI application authorization failed.
401.7 – Access is denied by the URL authorization policy on the Web server. This error code is dedicated to IIS 6.0.
403 – Access disabled: IIS defines a number of different 403 errors that point to a more specific reason for the error:
403.1 – Execute access is prohibited.
403.2 – Read access is prohibited.
403.3 – Write access is prohibited.
403.4 – SSL is required.
403.5 – SSL 128 is required.
403.6 – IP address rejected.
403.7 – Client certificates are required.
403.8 – Site access denied.
403.9 – Too many users.
403.10 – Invalid configuration.
403.11 – Password change.
403.12 – Denied access to the mapping table.
403.13 – Client certificate revoked.
403.14 – Reject directory listing.
403.15 – Client access permission is exceeded.
403.16 – The client certificate is untrusted or invalid.
403.17 – Client certificate has expired or is not in effect.
403.18 – The requested URL cannot be executed in the current application pool. This error code is dedicated to IIS 6.0.
403.19 – CANNOT perform CGI for clients in this application pool. This error code is dedicated to IIS 6.0.
403.20 – Passport login failed. This error code is dedicated to IIS 6.0.
404 – Not found.
404.0 – (none) – No files or directories were found.
404.1 – The Web site cannot be accessed on the requested port.
404.2 – The Web services Extension locking policy blocks this request.
404.3-MIME mapping policy blocks this request.
405 – HTTP predicates used to access this page are not allowed (methods are not allowed)
406 – The client browser does not accept the MIME type of the requested page.
407 – Proxy authentication is required.
412 – Prerequisites failed.
413 – The requesting entity is too large.
414 – Request URI is too long.
415 – Unsupported media type.
416 – The requested scope cannot be satisfied.
417 – Execution failed.
423 – Locking error.
5XX – Server error
The server was unable to complete the request due to an error.
500 – Internal server error.
500.12 – The application is busy restarting on the Web server.
500.13 – The Web server is too busy.
500.15 – Direct requests to Global.asa are not allowed.
500.16 — The UNC authorization credentials are incorrect. This error code is dedicated to IIS 6.0.
500.18 – THE URL authorization store cannot be opened. This error code is dedicated to IIS 6.0.
500.100 – Internal ASP error.
501 – The header value specifies an unimplemented configuration.
502 – The Web server received an invalid response while using it as a gateway or proxy server.
502.1 – CGI application timeout.
502.2 – CGI application error. application.
503 – Service unavailable. This error code is dedicated to IIS 6.0.
504 – Gateway timeout.
The 505-HTTP version is not supported.

Reproduced in: https://blog.51cto.com/cold2076goddess/1432464