Currently the File Format codelist is a subset of available mime types.
We can see no reason why this should not be the full set of available mime-type. However, our knowledge on this is sketchy, so we would appreciate community help on deciding if this correct and where we would find a definitive list. We would then see this as an 'external' list that is maintained by someone other than IATI.
This may be a useful start: http://en.wikipedia.org/wiki/Internet_media_type