I apologize if this has been answered somewhere else. I did a quick search and did not find it.
I just upgraded to Calibre 0.7.22. I downloaded a book from mobileread with a .prc ending. I changed the metadata and the line justification while converting it to .mobi. Then, I wanted to email the .mobi file to my kindle, but could find no way to select a specific format to email (using my firstname.lastname@example.org
address). The file that got sent to my kindle was the .prc file. Finally, I deleted the .prc from my Calibre library and that forced Calibre to send the .mobi file. I am just wondering if this is correct or if I am missing something.