Windows 7: Email messages sent via Windows Mail not received by certain domains

I just purchases a new DELL desktop system that runs Windows 7 and the newest version of Windows mail. My ISP is Comcast. Since using this Windows mail, people with email accounts on verizon.net and optonline.net do not receive my email messages when sent thru Windows mail. If I send these people the same message thru Comcast webmail the message is received by these people. Email accounts on yahoo, gmail, and various other servers can receive the messages. This leads me to conclude that there is something that Windows mail is doing to the outgoing message that is causing it to be rejected by certain servers.

Has anyone heard of such an issue or have any idea what the issue might be?

IS anyone getting your outbound windows mail?

Yes, I thought I said that.
Verizon.net, optonline.net and a private company server do not receive the messages.
Other comcast.net, yahoo.com, hotmail.com and gmail.com accounts do receive them.
When sent from the webmail application everyone receives the messages, so it is definitely a windows mail issue.

When mail doesn't go through there is usually an error message comming back to the sender. Have you received such an error? If not, it may be the email got through but was treated as spam by the recpient's email system. That's because sending it by webmail and sending by an email program on a computer produces different from information that may be treated differently on the receiving end.

I have received no error or undeliverable messages, and the messages are not i. The intended recipients spam folders. The messages are never received in any way shape or form. That is why I am asking. Has anyone ever heard of such a problem with Windows mail? I have tried everything on my end and a few of the recipients have checked extensively at their end but we cannot seem to find a reason.

It may not be the recipients filters but the recipients email service provider looking at all the "from" information. For example an email from obama@hotmail.com may be filtered out but the same email from obama@whitehouse.gov may be allowed to pass by the recipient's email service provider. The recipient may be able to fix it by going to their service provider's website and selecting a quarantine spam option and further adding the desired "from address" to the "allow" or "do not block" fields on the spam preferences webpage.

A better test (rather than comparing it to sending by web mail) would be to use a different computer (or even the same computer) running a different email program at your location for sending. As long as you are sending mail via the same service provider with the same SMTP account information, then it's a valid test of WLM versus another email program.

Not a problem on another computer. Don't have another email program on this one.
Question is Has Anyone Ever Heard Of An Issue Like This?!

What email program is the good computer running and are the smtp settings in the account properties set the same on both the good and bad sending computers?

The "good computer" is running Outlook Express and is on a Windows XP OS.
All settings are the same.

Any idea what could be causing this?

No. WLM on 7 is the replacement for OE on XP. Even though it adds many confusing features combined with a ribbon interface it still sends email via your sending account's smtp settings. However, the header information will be different. You can see the difference yourself by sending a blank email to yourself from the XP and the 7 computer. After opening the email look for "Properties/Details/Message Source". You can even copy and paste that text into Notepad and print it out for each. For example when I send an email using WLM 2009 it includes the line "X-Mailer: Microsoft Windows Live Mail 14.0.8117.416" and when I send an email from Vista using Windows Mail it says "X-Mailer: Microsoft Windows Mail 6.0.6002.18197". So it's possible for the receiving domain to filter out mail based on some line of the Properties text. I have no idea why they would do that based on the sending email program. However you will note that there are many lines in the properties data and there may be some other property they are filtering on. It might even be possible for you to change one of the sending options in OE so that emails sent to those domains will reject the OE mail as well. So if that's the problem, the solution would be to check all the sending options on OE and WLM and make them ecactly the same. Look at "Options/Send/Mail Sending Format".