Ubercart

Emails suddenly stopped being sent on my site too. Emails worked earlier this morning.

Not being sent to users with comcast or windows live email accounts:
Sitename: rolename role granted (to user)
Your order at sitename (to user)
Account details for username at sitename (to user)
Password reset (to user)

Still being sent:
New order at sitename (to admin)
Merchant Email Receipt (to user from Authorize.net)
Merchantname Customer Receipt/Purchase confirmation (to user from Authorize.net)

I reset my site to yesterday's snapshot - above emails from my site still not sent.

Things that happened around the time emails stopped working:
Changed my header for my email message in Authorize.net. Removed all changes later.
Edited user settings>Welcome, no approval required message.
Got a warning that there is a security update for my version of Drupal.
Edited invoice template. Later removed my changed file and put back original.

Troubleshooting ideas:
See if welcome message gets sent for new users admin creates. update: not being sent.
Install new dev of Drupal.
Looks unrelated, but check out: http://www.ubercart.org/forum/support/11237/order_notification_emails_ha...
Ran cron -> no change.
Sent a direct message from site email (not thru Drupal) to user -> ok.
Changed site email to cable host in case of blocked email problems -> no change.
Check out http://drupal.org/node/152803
Ran update.php -> no change
Disabled "secure pages" module -> no change.
Call my host.

Cannot run site with this problem.

What happened at your site around the time emails stopped working?

UPDATE: Welcome email is not being sent to users I have added manually! So, Ubercart may not be the problem, unless my settings have corrupted Drupal.

Troubleshooting update:
Added users.
The user with an email account though a webhost (hostgator) received the welcome email.
The user with an email account through cable service (comcast) did not receive a welcome email.
The user with with windows live account did not receive a welcome email early afternoon. Deleted this account and added it back later in the day. Now the welcome mail was sent to the live account. Password reset works for the live customer as well.

Comcast says that no emails have been blocked to any of my emails today; Nothing has been received though mysite.org.

myname@mysite.org emails are received by Comcast and Live.

UPDATE: My email problem seems to be due to Comcast:

Mail messages going to @comcast.net go to the spam folder if the message body text includes my site name "mysite.org" . This includes links, email addresses, reply header, etc. My site is not on any blacklists. I do not send out unsolicited emails. My site does not contain info that would be blocked by anyone. I don't have any suspicious emails in my sent folder. I'm still waiting for a callback from Comcast to resolve this.

Direct mail from webhost email account to cable email account works fine.