Uuencode (also called Uuencode/Uudecode) is a popular utility for encoding and decoding files exchanged between users or systems in a network. It originated for use between users of UNIX systems (its name stood for "UNIX-to-UNIX encoding"). However, it's available or easily obtainable for use in all operating systems and most e-mail applications provide it as an encoding alternative, especially for e-mail attachments. If you're sending e-mail with an attachment and you suspect your recipient(s) may not have a MIME-compliant system (for example, an older PC or UNIX system), you may want to specify "Uuencode" for the attachment to an e-mail note. (In Eudora, when writing a note, look for the little box set to a default of "MIME" and change it to "Uuencode.")
Basically, what Uuencode does is to translate or convert a file or e-mail attachment (it can be an image, a text file, or a program) from its binary or bit-stream representation into the 7-bit ASCII set of text characters. Text can be handled by older systems that may not handle binary files well and larger files can be more easily divided into multi-part transmissions.
If your recipent is likely to be on an older Macintosh system, you may want to try sending the attachment in another format called BinHex.
A popular program for encoding and decoding files in Uuencode format is WinZip, which is shareware that you can download from the Winzip Web site.