Again, I don't know exactly how it looks for a business account, but for my account, on
this page, you just enter whatever email address you like and that is what Plusnet will use. You can then forget about the Plusnet email address. When you say "the other being created from the application information", if that is the email address that was specified in the contact details when the account was applied for, it sounds like it's doing what you want anyway.
Kevin
plusnet Value Fibre
Using OpenDNS