Like many websites that you log into, MX automatically logs you out after a period of inactivity. That is not always immediately obvious, although we do display **server unavailable** where possible.

If you have logged into MX and gone to the Send page for example, MX will log you out, even though some functionality may still appear to be 'live'. 

The same will occur if you go to the Download page but don't actually download the data straightaway.

If you have a very large number of files to upload (1,000 or more), this will actually exceed the capability of the browser and also lead to a **server unavailable** message.
 In this situation, please compress the data first. See more info here.