Users of the widely used messaging service Gmail may be unable to access their emails on Monday, due to an outage that has made access to Alphabet’s communication platform unstable, with a 502 error message being displayed when attempting to access Gmail.

A number of Gmail visitors have found that they are unable to access the site at all on Monday, just as businesses in the US are beginning their workday. Instead of seeing their emails, they are greeted with a 502 error, temporarily preventing them from accessing their messages.

The problem does not appear to be a complete blockage of Gmail, but rather intermittent. Tests by AppleInsider staff have shown that access to Gmail is sometimes interrupted, both via a browser and through clients, for both free and paid accounts.

Although various Alphabet status pages do not indicate any issues, DownDetector reveals that many people have reported problems accessing Gmail services, with a sudden and definitive increase in complaints.

A 502 error is an HTTP (Hypertext Transfer Protocol) error code that indicates that the server received an invalid response from another server that it considers to be a proxy.

In other words, a 502 error occurs when the server on which a website is hosted is unable to obtain a valid response from the proxy server it uses to process user requests. This can happen due to a connectivity issue between the two servers, or due to overload or saturation of the proxy server.