I have installed many mambosites in my hosting.
And this is the behavior for the mailing options.
contact form= working ok
mail to a friend= working ok
mass mail = working ok
registration form= working ok(*)
(*) registration form sends mails ok, excepting to my own email address..!! 
when i register with the address:
julior@cableonda.net I do not get any confirmation mail
But when I ask for a new password for
julior@cableonda.net, I get it without problems.
If set the contact form with
julior@cableonda.net, i get the mail. If I send a news to julior.. I get it.
It means that is only at the registration form.
I will highly appreciate your comments