It appears that GMail has been having some issues lately with users receiving a 404 error while trying to login. I think most people have experienced this kind of error at some time or another. This situation is a little different because people are claiming that the emails that were sent to them during the outage do not show up. It could be possible that the GMail server is holding the emails until they ensure the user’s access has been restored but some people think that they are permanently gone.
Hopefully this doesn’t become a common issue because I have read quite a few horror stories about GMail losing messages or even deleting everything a user has! If you want to read some of the stories then search Google for “GMail Horror Stories“. I have had no issues but I hope I don’t jinx myself.