The option that file navigator is used to show eml files is enabled. However, when trying to open an .eml file from within the File Navigator (e.g. by double clicking) the file opens with the eml viewer set up in the OS. I.e. if there is no default eml viewer nothing happens or the eml file opens in the application defined in the OS.

I tested this with LN 8.5.1, 8.5.1FP5 and 8.5.3 with Win XP SP3, Win7 SP1.