Manual:$wgSend404Code

Output: $wgSend404Code
Send 404 HTTP status for not found pages.
Introduced in version:	1.19.0 (r105645)
Removed in version:	Still in use
Allowed values:	(boolean)
Default value:	true
Other settings: Alphabetical | By function

Details

Web servers are supposed to send 404 responses for any not found page. If someone tries to load an article that doesn't exist, MediaWiki sends a 404 status. (Note, editing an article that doesn't exist does not send a 404 status) Some webservers try to intercept 404 responses and give "helpful" 404 response pages, which is quite annoying. Some webservers get the 404 intercepts severely wrong, causing garbage to be output. In either case, you should consider looking for a new web host, but if that's not an option then this setting can work around the issue.

In cases where for technical reasons it is more important for MediaWiki to send the correct status code than for the body to be transmitted intact, this configuration variable is ignored

Changes

Since MediaWiki 1.28 this setting also affects status code of "action=history" if the page is not there.