Originally Posted by tomsem

I am coming to the conclusion that you need to send only files that have either just mobi, or hybrid files with both mobi and kf8. If I process a hybrid file to extract just kf8 that is rejected, though it works if side loaded. An exception might be fixed layout kf8 as there is no mobi equivalent of those. I've been using the Send To Kindle app, not email attachments, but both probably process the same.

I'm also seeing a couple of cases where a hybrid file is accepted, but the font size gets bumped up 2 or 3 notches. But most of the time it works okay.

I'll be investigating both issues when I get a chance. It occurs to me that one could generate a hybrid file whose mobi segment is vestigial (i.e. create media queries that basically leave no content in the mobi segment. Maybe those would be accepted.

I do have a few files that are too big to send to PDS (limit is 50MB) and had hoped to split some of them so I could store separate mobi and kf8 files, but that does not appear to be possible. I might have to figure out how to split the books into 'part 1' and 'part 2', etc. Even with Amazon content, reflowable content always is available to apps and devices that don't support kf8.

Note that while hybrid files are stored in your personal documents storage, what gets downloaded is just the segment that your device or app understands.