Hey all again,
Ok, I have another update, I am now able to log into the UebiMiau, and found that I could change the settings manually in both webmail clients to show the proper e-mail address and name:
Aaron Murray <firstname.lastname@example.org>
However it would be a lot nicer if it took the ISP User/Email & Settings information (Real Name and Email Address settings) and populated the webmail script settings with that information automatically, rather than having to do it manually for each user added.
And I still don't know why it is adding 4 lines to the /etc/postfix/virtusertable file for each email address, is there some kind of problem with my settings somewhere?