A file decompression utility can normally decode a MIME file if an email program does not recognize and decode the file automatically. A few programs that open MIME files include Mozilla Thunderbird for Windows and Mac OS, KMail for Linux, Apple Mail and Microsoft Outlook 2013.
MIME, which is an acronym for multipurpose Internet mail extension, is a type of encoded extension used by email programs to support file attachments. These files are most often recognized with a .MIM extension, but they may also be sent as MIME. Standard emails attachments use a seven-bit format, but MIME files contain eight-bit encoded data containing characters not included in the U.S. ASCII character set.
In addition to text, MIME extensions also support images, audio, video, application programs and a host of other types of data. The vast majority of human-written emails are transmitted to their destination in MIME format.
The idea for MIME files was first proposed by Nathan Borenstein in 1991 because email programs were unable to process and transmit any data other than ASCII text. Originally designed chiefly for SMTP protocol, its use has expanded to describe the type of email content being sent as well as provide a content-type description for the Web.