The MIME type application/x-trash is used to denote the presence of backup files. The category of this MIME type is "application".

These are files that are used to create backups of important files automatically. Usually these are the older files themselves that are copied and saved with a different extension. Some of the most common files that this process is to done to include the autoexec.bat files that is found on the Windows Platform.

These files usually use the following file extensions - %, ~, OLD, BAK. Most of these files are deleted immediately upon detection by some systems. This is done because they are known to occupy unnecessary space within the system. These file types are also often earmarked for being prone to malware. Many different types of malware also try to infiltrate a system in the form of one of these file types.

These files are often thus considered to be redundant and high-risk by mail systems and security applications. Users should always be wary of receiving files like these from external sources. There is a high probability that such files are actually malware because these files are usually not created or transported beyond area of their intended use.