Can't delete admin Mail account

Question

OS 10.3.9 Mail 1.3.11
G4 with a single admin account. The Address book is empty. One POP3 and a .mac mail account for the admin. No sig cards. I want to delete the admin's Mail account(s). I'm basing things on the following statement in Mail Help
"The first time you open Mail, it automatically sets up accounts for you using the information from the .Mac pane of System Preferences and the Setup Assistant. If no information is found, you will be prompted to set up a new account."
I figure that if I delete all the admin's mail accounts and then Quit Mail then the next time Mail is launched it will prompt for a new account. Not! Looks like I can't seem to attain the "no information found" state. Here's what I've done.
Mail:Preferences:Accounts
Shows 2 accounts - one for POP3 and one for .mac
Selected each and clicked "-". All accounts deleted.
Quit Mail and re-launched it.
Get a prompt asking if I want to import mail. I say No.
Mail:Preferences:Accounts
The same 2 accounts are back again - does this over and over
I go to the .Mac Pane of System Preferences
The .Mac tab shows some values for Mac Member Name and Password
I delete the values and close the .Mac Pane
Launch Mail again
Mail:Preferences:Accounts
Now only the POP3 account shows up - so I got rid of one of them
No matter how many times I delete the POP3 account, it is regenerated the next time Mail is launched. Evidentally when Mail is launched, it finds my e-mail address, password, user name, Full Name, and server values - so it automatically regenerates that account. But where does it find it, and how can I get rid of it? And what/where is this Setup Assistant the Help message refers to?
I'm giving this G4 to another, with a sanitized 10.3.9 (to remove all traces of me), and I want Mail to prompt the new owner for a new Mail account so that he can populate it with his own information. But instead, it rebuilds my old account. Not sanitized enough yet. Maybe the mysterious Setup Assistant remembers old values somehow?
TIA
Eric

Answer 1

Here's the complete picture. The G4 internal drive has OS 9.2.2. An external FW drive attached to the G4 has 10.3.9 (G4 boots both). The plan was to clean/sanitize 10.3.9 and then, from 10.3.9, use SuperDuper! to clone it to another partition on the FW drive. Then erase the internal OS 9.2.2 disk and then restore the 10.3.9 clone to the internal G4 drive. The FW drive will not be given to the new person. SuperDuper! ignores deleted files so the resulting internal 10.3.9 drive in the G4 will have no sectors with deleted information that could be subject to data mining. Not exactly a clean install but hopefully not harmful.
I have the Panther install disks but they only install 10.3.3 and I don't want to go through the effort of downloading the huge combo updater again and applying it. Thought it would be easier to do an "approximate clean" install of my current 10.3.9 to the G4's internal disk. However, this problem with the Mail setup assistant has me worried. Even if I could get rid of that problem, I now worry that there will be still more sensitive artifacts laying around in the existing admin's home directory.
So, I plan to boot into the 10.3.9 clone system, create a new account and give it admin authority, and then delete the old existing admin account to get rid of its home directory . I'll delete SuperDuper! on this clone as well. The resulting 10.3.9 clone will then be restored to the G4 internal drive.
At this point it is mainly intellectual curiosity that drives me to solve the setup assistant problem. The nerve of that thing to resurrect old deleted account information rather than letting me build a new account with different information.
Thanks for your time.