Authentication has nothing to do with deliver-ability.
Authentication implies the connection to the email server that sends the email, not the the email itself. The outgoing email is not somehow authenticated in this process. Use the mail option if it works. You aren't going to have any better success getting email delivered with pear and you will probably have to jump through hoops to get it configured.
SPF and DKIM are the best options for including deliver-ability, and they don't require PEAR.