> So I downloaded a version 8.5.3 and this time it behaves as expected (with and without MIXUPDATES) as the file appears as binary data in the raw folder.
> I suppose there has been some kind of fix between the two versions. Could this be?

Wow. I guess so ;) I remember we fixed an issue regarding multipart messages, maybe that was related.

Thanks for reporting the positive outcome back to us!

Christian