Users of some email clients and operating systems may find the 'mbox' format more suitable for folder archives than the compressed files format provided by FastMail.FM's 'Archive' action. If you want to get an mbox archive of your FastMail.FM folders, you can now use utilities provided by FastMail.FM users written in Ruby or Unix shell. These will both work on Linux, MacOS, and Windows (Windows requires installing Cygwin).