Comment 7 for bug 1949604

No, if you havent setup a mail relay it will just send the mail directly
from your computer. This is pretty fragile as amazon is quite likely to
block mail from random computers. I suggest setting up a mail relay, you
can do so for free with a hotmail account. See
https://manual.calibre-ebook.com/faq.html#i-cannot-send-emails-using-calibre