Thanks Lowell. Yes, I think I read one of those last night, plus several posts in other MS related forums regarding this file and the "Safety Net" feature within MS Exchange 2013.
My questions to MS are around: is it actually sensible to restore "mail.que" (and it's friends) in a full DR server recovery scenario, i.e. might we be ill-advised to restore this file and associated files? i.e. in my mind it's not just about is it ok to exclude, but also is it bad to restore it... i.e. the distinction between "ok/safe to exclude" versus "bad to restore".