When your website is temporarily unavailable due to server maintenance or migration, it is important to return an HTTP 503 (Service Unavailable) status code along with a helpful message. This status code informs search engine crawlers that the downtime is temporary and that they should come back later instead of indexing the unavailable pages. Avoid returning a 200 status code during downtime, as this causes crawlers to index maintenance pages, which can harm your site's SEO. Proper use of the 503 status code helps maintain your site's search presence and prevents indexing of irrelevant content during outages. [Google]