Can't send ebook by email to kindle

[Elpinche]

I have caliber 2.53 [64] bit in a windows 7 HomePremium computer. I've setup the email in Preferences>sending book by email. I have tested it using both @gmx.com and @hotmail.com adress and both test come out succesfull (I can see the emails in the sent folder of my email accounts) but whem I try to send a book it fails with either account. This is error log.

Sending failed...

Traceback (most recent call last):
File "site-packages\calibre\gui2\email.py", line 43, in run
File "site-packages\calibre\gui2\email.py", line 130, in sendmail
File "site-packages\calibre\utils\smtp.py", line 138, in sendmail
File "site-packages\calibre\utils\smtplib.py", line 738, in sendmail
File "site-packages\calibre\utils\smtplib.py", line 504, in data
File "site-packages\calibre\utils\smtplib.py", line 329, in send
SMTPServerDisconnected: Server not connected

Job: "Email BOOKTITLE to XXXXXXXXXX@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 98, in __call__
SMTPServerDisconnected: Server not connected

I disabled my windows firewall completely, and disable the firewall in my router, I also don't have an antivirus in this computer.

[Elpinche]

I solved it!

I went to my router settings and under the firewall tab, there is the option to turn of the firewall (a checkbox) but there are other options like: DoS Attack Protection,Block Pings, IPSec Pass Through, PPTP Pass Through, L2TP Pass Through, Block Fragmented IP Packets. So in desperation I turned all of them off (previously I only turned the Firewall Enable/Disable off) and it worked. I can send books to my kindle now.

Since the problem seemed to be my router, I turned my windows Firewall ON again, and even then I can still send books. So the culprit seems to be one of those options in my router. I'm going to play with the options to see which one or which ones are the ones that make it fail.

EDIT: The options that make it so it fails to send the book to my kindle are: IPSec Pass Through, and/or Firewall Enable/Disable.