Nice to read an article on the Internet that promises so much, yet left out so much detail.

e.g Further clarification is required here:

"The next two lines define an account we'll set up that will have permission to access the mailboxes. Yes, one account will have the ability to read all the virtual email. Yes, this can be considered a security problem. Please do your best to ensure no one can become this user. We'll call the account "virtual". Add it any way you want to the system (eg, useradd) and make note of it's uid and gid.

The final line specifies a text file where we can place aliases for virtual accounts. The contents looks like this: