550 SMTP Authenticate

Hello All,
I'm getting the above message when trying to send e-mails from my home pc, I've added a Digital ID plus a user name and password, any help please...

Never needed to do this but from a google search...

'To configure Outlook or Outlook Express to authenticate, click on Tools, then Accounts. From the Accounts window, click on the Mail tab. Click one time on the account entry and then click on the Properties button. Click on the Servers tab and check the checkbox labelled "My server requires authentication" and click on Ok.'

Try sending a message without the digital signature as a test - to see if the problem is actually related to the digital signature.

Are you using as your SMTP server your isp's smtp server ?
You should be using this as your outgoing server rather than your mail providers