Override mime type based on file extension

[Robert Nelson <rnelson@xxxxxxxx>]

Is there an easy way to override the mime type based on the file extension of an attachment?

 

Currently .diff files show up as mime type application/octet-stream and I’d like them to be treated as text/plain.

 

I could probably do this by writing my own filter for application/octet-stream but was hoping there was a simpler way.