Email to Kindle not working

Hi all,
I know this is a common problem but I can't get Calibre to email a book to my Kindle.
I am running 64-bit Windows 7 Home Premium and am running Norton Security Suite. I have checked the Norton firewall and made sure calibre is allowed access through the firewall. My email provider is Comcast.
I have checked my Kindle account on Amazon and allowed my email address as an allowed email address.

The error message I get from Calibre is as follows:

calibre, version 0.8.59
ERROR: Failed to email book: <b>Failed</b>: Email The Blade Itself to djkoble_65@kindle.com

Starting job: Email The Blade Itself to djkoble_65@kindle.com

Sending failed...

Traceback (most recent call last):
File "site-packages\calibre\gui2\email.py", line 37, in run
File "site-packages\calibre\gui2\email.py", line 112, in sendmail
File "site-packages\calibre\utils\smtp.py", line 93, in sendmail
File "site-packages\calibre\utils\smtp.py", line 85, in sendmail_direct
IOError: Failed to send mail: SMTPServerDisconnected('Connection unexpectedly closed',)


Retrying in 1 seconds...


Sending failed...

Traceback (most recent call last):
File "site-packages\calibre\gui2\email.py", line 37, in run
File "site-packages\calibre\gui2\email.py", line 112, in sendmail
File "site-packages\calibre\utils\smtp.py", line 93, in sendmail
File "site-packages\calibre\utils\smtp.py", line 85, in sendmail_direct
IOError: Failed to send mail: SMTPServerDisconnected('Connection unexpectedly closed',)

Job: "Email The Blade Itself to djkoble_65@kindle.com" failed with error:
Traceback (most recent call last):
File "site-packages\calibre\gui2\threaded_jobs.py", line 83, in start_work
File "site-packages\calibre\gui2\email.py", line 92, in __call__
IOError: Failed to send mail: SMTPServerDisconnected('Connection unexpectedly closed',)

Called with args: (u'C:\\Users\\Dennis\\AppData\\Local\\Temp\\calibr e_0.8.59_tmp_xlnlhf\\rnscldcaltmpfmt.mobi', u'The Blade Itself - Joe Abercrombie.mobi', u'djkoble_65@kindle.com', u'E-book: The Blade Itself', u'Attached, you will find the e-book\n\nThe Blade Itself\n\tby Joe Abercrombie\n\nin the MOBI format.') {u'notifications': <Queue.Queue instance at 0x0951DF58>, u'abort': <threading._Event object at 0x094F5630>, u'log': <calibre.utils.logging.GUILog object at 0x094F5830>}

Any help anyone could give me would be appreciated as I currently have to manually connect my Kindle to the computer via a USB connection which is inconvenient.
Thanks,
-Dennis