What is a 5xx Error?
A 5xx Error is any type of server error. The name 5xx refers to a HTTP Status code in the range of 500-599, which are all different types of server errors.
500 (Internal Server Error): This is a general message that means something is wrong with the server, but no further information is available. Common explanations for 500 errors include coding errors in application code or configuration files, file permissions issues, exceeding memory limits, or even server timeouts.
503 (Service Unavailable): Typically a temporary issue and is usually caused by server overload or system maintenance. If a site suddenly has a very large influx of traffic, it could cause the server to go down and return a 503. Similarly, when a site needs to perform maintenance on their servers, they will typically return a 503.
Why It's Important
5xx errors on your site are a big deal. They are perhaps the highest priority issue on your site and should take first priority in your SEO efforts.
First of all, the page's content is not available to search engines, so they will not be included on search engine results pages and you won't have any chance of getting organic traffic to this page.
Thankfully, search engines typically understand that 503 errors are usually temporary. So instead of immediately removing these URLs from their index, they will give the site some time to recover and return in a few hours or days. It's possible these pages could suffer a short-term rankings problem, but will general come back quickly after the issue is resolved.
On the other hand, a 500 error, a sustained 503 error, or other 5xx errors are less forgiving and could result in the page being removed from the search engine's index.
By resolving these issues in a timely manner, you can minimize the chance that these URLs will be ranked poorly or removed from the index completely.
How to Fix
Since HTTP 5xx errors can be a bit complex, technical, and specific to each server or application, it's not possible to list specific instructions to fix the issue.
The most common causes of these errors are either a coding error in the application or configuration files, server overload, or site maintenance. Whichever is the case, contact your webmaster or server administrator to resolve the issue as soon as possible to minimize the impact of such problems.