For my incoming mail folders I use names that start with `IN'.  For
example, I put mail sent to the procmail mailing list into a folder
named IN.procmail.  This way when all my folders are listed
alphabetically the incoming folders are together and near the top.
They are near the top because Unix is case sensitive and upper case
letters come before lower case letters in an ascii sort.

Of course, you can use any names you like for your mail folders!