Has anyone transfered e-books to their kindle?

I’m trying to use Calibre to transfer mises.org ebooks to my kindle and i keep getting an error

ERROR: Failed to email books: Failed to email the following books:

Time Will Run Back

Failed to send mail: error(10054, ‘An existing connection was forcibly closed by the remote host’)
Traceback (most recent call last):
File “site-packages\calibre\gui2\device.py”, line 505, in _send_mails
File “site-packages\calibre\utils\smtp.py”, line 82, in sendmail
File “site-packages\calibre\utils\smtp.py”, line 74, in sendmail_direct
IOError: Failed to send mail: error(10054, ‘An existing connection was forcibly closed by the remote host’)

Anyone else know how to fix this?