If you have to take a site down for some type of unavoidable maintenance task (and it's not a big enough site that you have a backup server), what HTTP status code should you have your server return to minimize the possibility that search engines will think the site is gone?
I found this list of status codes from W3C, of which the following seem applicable:
- 503 Service Unavailable
- 500 Internal Server Error
- 408 Timeout
- 404 Not Found
I think 503 is the most appropriate, but I don't know what search engines might prefer.
From the horse's mouth: