[MlMt] Hijacking field for "Due Date"

[Zvi Biener]

Hi Folks,
I'd like to be able to associate a due date with email messages. 
Currently, I can do this through tags, but if there are multiple tags 
already associated with a message, it makes sorting difficult. Is there 
an imap field I can perhaps hijack in order to do this? The field can be 
local only - synching with the server would be nice, but not essential.
Thanks,
Zvi