The transport system that moves email around the Internet can sometimes garble a message containg an attachment such as an image or audio file.
Mpack for UNIX
Not all email programs support the MIME standard, making it difficult for many email users to deal with encoded documents sent to them. The system that transports email from one computer to another is known sometimes to be unfriendly to non-text information such as images, which is why MIME includes an encoding/decoding mechanism that converts arbitrary information to text and back. This encoding mechanism is known as base64, and seems to be the source of much frustration for many email users using non-MIME compliant software. If your email software does not support the automatic decoding of base64-encoded documents, then you will need to get your hands on a utility to help you out. I highly recommend mpack. The mpack distribution actually includes two programs: mpack, for encoding images, files, etc. into base64 for sending; and munpack, for decoding images, files, etc. that have been received. mpack is available for DOS, Windows, Macintosh, UNIX, and a few other platforms. Click here for the Mpack FTP site.
From the Mpack FTP reository: mpack 1.6 is a unix only "maintenence" release. It adds no new features. Users of other platforms supported by mpack 1.5 should continue using it. The various security patches have been incorporated, as has a patch that fixes the handling of ';'s in attachment filenames