When you first sign up to Redbrick and your account is created, all mail sent to your Redbrick email address is forwarded to your DCU email address.
While this is in place, there won't be a Mailbox for you on Redbrick's servers. Your mail will not be stored on Redbrick so you will be unable to use Redbrick webmail to access your messages.
If you want to disable email forwarding for your account, there are 2 ways to do this:
Once this is done, the next piece of mail to arrive should create your Mailbox on redbrick, and you will be able to access your mails using mutt or via the webmail interface.
Setting your redbrick email to forward to another address is quite simple.
Create a file in your home directory called '.forward' and put the email address you want your mail to forward to on the first line. If you want to keep a copy in your redbrick mailbox too, you can add \username on the next line (where username is your redbrick username.
Save the file, and email forwarding should now be active.
To quickly set up forwarding you can also type:
echo "email@example.com" > ~/.forward
at your shell and it'll all be done in one step.