Originally Posted by cdnchef76
Thank you, now I understand.
The receipes were generating EPUBs but the Auto-Send formats only included AZW, MOBI, TPZ, PRC, and AZW1. When I added EPUB the list, the email was automatically sent correctly. Unfortunately, my Kindle can't read EPUB files. Is there a way for me to have the EPUB automatically converted to MOBI prior to it being sent?
To expand on Kovid's question:
In Preferences -> Interface -> Behavior, change Preferred output format
from EPUB to MOBI.