This what I am finding by going back to the old Outlook profile. The current status is, I have one email account for a GoogleMail account and I had one for BT which has now been deleted. There are two folders linked to two different pst files one for Googlemail linked to a Google Mail Account and another for BT Mail not linked to an email account because it has been deleted.

>>> If I send myself an email to the Google account, it comes from the BT internet address because it was once the default address even though the BT email address has been deleted. BTW, this should be impossible but it is happening. I cannot find a way of changing the default.

>>> If I try to create a new BT Email address, Outlook I get this message:
Send test e-mail message: Cannot send the message. Verify the e-mail address in your account properties. The server responded: 530 authentication required - Your email could not be sent. To fix this you must make a simple change to your email client (known as SMTP authentication)

At least with this profile, I can get one of two email addresses to work but it is not ideal.