Thanks for the 'full story'. Unfortunately, it's got me totally confused!
I was assuming that you were trying to enter the information into the accounts settings of Outlook (or Outlook Express, Thunderbird or any other email client). However, your latest post suggest that you're trying to set up the account 'at the other end', by entering information into an online form. The reason that's got me confused is that the service provider will know what their own server addresses are, so I can't see why you should need to enter them into a form on their website.
If you've bought the domain name 'www.newname.co.uk' and paid for a POP3 email service to go with it, you shouldn't need to do anything 'at their end' (apart from reading the information that you'll need to enter into your own email client). The new account should be automatically created. Any mail sent to
[email protected] or
[email protected] or
[email protected] should find its way to your space on the provider's server. You then just need to set up Outlook (or your alternative email client) to receive mail from each of those account names. (i.e. all of the work should be at 'your end' rather than at 'their end'). All that you should need to do is to read the POP3 and SMTP details on the provider's website and enter them (together with each mail address) in your mail client.
I'm not sure whether that will help or not. If you can find the POP3 and SMTP server addresses on the provider's website, go to Tools > Accounts > Add > Mail in Outlook Express. (It's roughly the same in Outlook and, I believe, in Thunderbird). Try setting up the account solely at your end and then try an email to yourself at your new address. You might find that it works anyway.
Chris