The GMail service has been flaky since the past few hours and all you see is the following 502 server error message:
We're sorry, but Gmail is temporarily unavailable. We're currently working to fix the problem -- please try logging in to your account in a few minutes.
If the downtime is affecting your work, here's a simple trick to access your GMail inbox.

You can download all your unread Gmail messages using a desktop client like Microsoft Outlook or Thunderbird even in situations when normal web-access is unavailable.

Check the screenshot below: GMail website is returning an error message but the Outlook send/receive window is busy download the emails locally.

GMail Server Error

Never miss Gmail again.

Also read: Solutions to GMail Login Problems