I'm trying to configure my Outlook Express V6.00.29... to receive/send messages via Hotmail. I thought I had it sorted out, as OE receives messages without problem. However today I tried to send a couple of messages, and it failed, returning the following error:

'The message could not be sent because the server rejected the sender's e-mail
address. The sender's e-mail address was '{removed email address}'. Subject
'{the subject of my message]', Account: 'Hotmail',
 Server: 'smtp.live.com', Protocol: SMTP, Server Response: '550 5.7.3
Requested action aborted; user not authenticated', Port: 25, Secure(SSL):
Yes, Server Error: 550, Error Number: 0x800CCC78'

I was looking around on Google and on your site here, and came upon this suggested solution (re: port errors) which sounded worth a go.

/solutions/settings/archive/2009/01/06/send-and-receive-windows-live-hotmail-emails-from-a-mail-client.aspx

However I tried it, and I received the following error on sending a message...

The message could not be sent because the server rejected the sender's e-mail
address. The sender's e-mail address was '{removed email address}'. Subject 'test',
 Account: 'Hotmail', Server: 'smtp.live.com', Protocol: SMTP, Server Response:
 '550 5.7.3 Requested action aborted; user not authenticated', Port: 587,
Secure(SSL): Yes, Server Error: 550, Error Number: 0x800CCC78

So more or less the same error, just the revised port, and you will see I was toggling between starting my e-mail address in upper/lower case (in the Tools/accounts/mail/properties...) in case it might be case senstive.

Any advice would be gratefully received. Please remove my address from the two error messages above.

Thx! JW

Hi JW, 

After reviewing the error message that you posted, I've verified that the issue you're experiencing is due to an incorrect POP3 setting in Outlook Express. To correct this issue, I recommend that you reconfigure your account in Outlook Express by following the steps here:  

http://windowslivehelp.com/solutions/settings/archive/2009/02/18/how-to-add-your-e-mail-account-to-microsoft-outlook-express.aspx 

Note: Make sure to check the box that indicates that your outgoing server requires authentication (in most e-mail clients, this is not checked by default). 

FYI: Before removing your account from Outlook Express, ensure that you have left a copy of your messages online or have created a backup. Otherwise, reconfiguring your account in Outlook Express may cause you to lose your messages.

Thank you very much, that seems to have fixed it.

Step 9 from the posted link, was new, and a change, and seems to have made the difference.

I appreciate your help a great deal.

JW