On 5.8.x emailed .mobi recipe files show the date under the resulting .pobi files when they show up on the Kindle. These files are located under "docs" not "periodicals".
On 5.8.x manually transferred .mobi recipe files are located under "periodicals" and ordered by date as expected.
On 5.9.x emailed .mobi recipe files show the author "calibre" under the resulting .pobi files on the Kindle. These files are located under "docs" not "periodicals".
On 5.9.x manually transferred .mobi recipe files are located under "periodicals" and ordered by date as expected.
So it follows that Amazon changed how emailed .mobi files are handled in 5.9.x to the detriment of Calibre recipe files. Either stay on 5.8.x if you can, manually transfer, or send feedback to Amazon
kindle-feedback@amazon.com notifying them that you're unhappy with the change.
Kovid--Is there anything that can be done with the metadata on the Calibre side in the interim that will allow for emailed files to populate the date field rather than the creator field?
Thanks.