553 SMTP Errors with Outlook 2003 - tried everything else!!?

I've had this problem for about the last 10 days and it seems that a few others have as well. The errors message is:


Task 'Yahoo! - Sending' reported error (0x800CCC0F) : 'The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP). The server responded: 553 From: address not verified; see http://help.yahoo.com/l/us/yahoo/edit/al...

I've checked all my settings, applied the Office 2003 Service Pack, switched the smtp server to my ISP's (Orange) but none of these seem to help.

Anyone got any ideas?

I've tried Sonkysst's suggestions but still getting the same problems.

I've also tried Thunderbird with exactly the same settings and its working fine!?

Is there anything else I can do?

Method 1. Enable authentication
To enable authentication:1. Start Outlook 2003.
2. On the Tools menu, click E-mail Accounts, click View or change existing e-mail accounts, and then click Next.
3. In the Name column, click the required e-mail account, and then click Change.
4. Click More Settings, and then click the Outgoing Server tab.
5. Click to select the My outgoing server (SMTP) requires authentication check box. If the SMTP server is different than your incoming mail server, go to step 6. If your incoming mail server is also your SMTP server, click Use the same settings as my incoming server. Go to step 7.
6. If the SMTP server is different than your incoming mail server, follow these steps:a. Click Log on using.
b. In the User Name box and the Password box type the appropriate user name and password.
c. Click to select the Remember password check box.

7. Click OK, click Next, and then click Finish.
8. Send the e-mail message. If this method does not resolve the issue, go to "Method 2. Verify that the correct server is configured."



Method 2. Verify that the correct server is configured
If the ISP and the e-mail provider are different entities, you must configure the name of the ISP server in Outlook:1. Start Outlook 2003.
2. On the Tools menu, click E-mail Accounts, click View or change existing e-mail accounts, and then click Next.
3. In the Name column, click the required e-mail account, and then click Change.
4. In the Outgoing mail server (SMTP) box, type the name of the ISP's server. For example, you might type ISP_Server.contoso.com. You can also type the IP address of the server.
5. Click Next, and then click Finish.
6. Send the e-mail message.