How can I configure mutt email client to use koi8-r character encoding?

“mutt charset koi”
“mutt sending mail in iso-8859-1”

To make mutt use koi8-r encoding edit your muttrc file (usually /etc/Muttrc or ~/.muttrc) and add line set charset="KOI8-R" for reading and line set send_charset="KOI8-R" for writing in koi8-r character encoding. Your terminal program and your editor should be configured for koi8-r encoding independently/separately.

What does the “application/msword antiword” mean in the mailcap file?

“mailcap application/msword antiword”

Mailcap file (usually /etc/mailcap or ~/.mailcap) is the file, which is used by many email clients. This file specifies how application, such as email client, should handle a certain type of file (usually attachment). If mailcap contains the line which looks like application/msword; antiword %s , then programs, which respect (either use) this file, will run program called antiword, giving it current file as a parameter. Antiword is a program which converts Microsoft Word files into plain text, therefor makes them readable without using any Graphical User Interface (GUI). Antiword can be downloaded from the site of it’s author.