The xmh program is usually installed with other X clients. Because it also uses some MH commands, it needs access to MH files and commands.
xmh uses a few special files (for simplicity, the Figure Important parts of a UNIX filesystem doesn't show them). xmh makes a file called .xmhcache in each folder that you select. The file keeps a scan listing of the messages in the folder.
xmh uses the draft folder, too. It also makes temporary draft messages in files named xmhdraft0 through xmhdraft9 in each user's MH directory. When a draft has been sent, it's renamed with a leading comma -- for example, ,xmhdraft0.