Compose Mail As setting won't stay

[viable]

I try to set the mail we compose as "HTML", however when I set this and then save the preferences to import them on a different machine, I find that my setting reverts back to either "Enriched" or "Plain". Importing the preferences back into the same machine always puts the compose to "Plain". Where is this preference kept (file/folder/registry)? perhaps in the short term I can manually keep this setting.