Assuming that you have setup your Outlook Express software correctly (check our Outlook Express Setup Guide) and you have opened your firewall to Outlook Express, the most likely cause of your problem is that you have an email sat in your Outbox that was written when your Outlook Express was NOT setup correctly.

If our relay server sees an email trying to be sent that has not got a valid 'from' address, it will reject it with the error message above. So, delete ALL your emails that are sat in your Outbox, check your settings (make sure your email address is set correctly as anything@yourusername.plus.com with no spaces or anything before or after it). Then re-write the emails you're trying to send.

If you have a problem when sending email from Outlook 2002 (e.g. your email is being sent correctly but stays in your Outbox, or messages complaining that the server disconnected or timed out), disabling SMTP authentication may help.

Check you are not using authenticated SMTP which may cause problems with sending.

In Outlook Express:

1) Click on Tools (top menu)
2) Click Accounts
3) Select the Mail tab
4) Double click on your email account (in the account window)
5) Select the Server tab
6) Check that My server requires authentication is not ticked.