Is there any way to turn off the automatic e-mail that is sent to the user when their mailbox is created? If not, where can I change the text it sends?
You can change the text of the welcome email that is sent to new email accounts in the Language Editor (System tab) under mail > en_mail_user.lng (the fields are welcome_mail_subject and welcome_mail_message).
That's a good question. To be honest, I can't tell. Till knows it, but he's not available right now...