Intermitant Outgoing Emails Do Not Send


Sep 20, 2012
I'm out of ideas. Please help!

I manage the computers in our facility and one of our users has a comcast account that she have been using for years, but starting roughly 4 months ago--her emails intermitantly send out. As far as I an tell, she receiving all incoming mail.

Here is the scenario:

She only uses one email, in she uses Windows Live Mail.
She is a one-on-one private teacher that emails out her assignments at the end of each day that she teaches.
She emails roughly about 10 emails or so at the end of each day, all with the same subject, but different attachment.
She does not email in bulk, she only sends 1 or 2 attachments at a time and sends to only 1-3 contacts per email.
Attachments are tiny. Each .doc is only 10-20 kb per file.
It seems there is a trend there is always an attachement when it doesn't send.
She has Windows 7 64bit, tried in both Windows Ultimate as well as Windows Professional.
Sometimes it doesn't show in the sent folder, and sometimes it does.
Not specific to a domain, like @gmail, @yahoo, @hotmail, etc. (as far as I can tell)
Some emails send. Some emails don't.

The emails look similar to this:

Subject: Week 13 Assignment

Please open attachment.

What I have done to try to fix the problem:

- I've replaced the wireless router.
- I've relocated the wireless router to a better, higher, cooler location.
- I've replaced her computer.
- I've tried to plug in directly to the modem.
- I called comcast to make sure there wasn't any connectivity issues on their
- Ensured that the router'd capacity wasn't reached (like too many devices connected)

- I have done a clean OS re-install to make sure that it was not a virus.
- I have tried both Windows Ultimate 64bit and Windows Professional 64bit
- I tried it in Windows Live Mail, Outlook 2010, Mozilla Thunderbird, and online.
- I called comcast to make sure there wasn't any limitations that we were hitting or coming close to.

Email Settings
- It is not going into spam.
- It is ONLY THAT comcast account.
- I've quadruple checked POP3 and SMTP settings in Windows Live Mail.
- A majority of the emails get sent to gmail, yahoo, hotmail, and msn.

Question in addition to solving this problem:
- Could an email successfully send and while a recipient never get the email in their inbox, nor spam?

I can't seem to remember everything I've done since it has been so long since we've had this problem, but I'll be happy to answer any questions that may arise.