During the setup of wordpress, I realized that registration emails were sent out with a strange login(at)box
Basically, when you set up wordpress on bluehost, the From address in the mail your users will receive when they register is the default “catch all” provided by bluehost as your login unless you create a wordpress@your_site email address from the cPanel. After you create the wordpress mail account, the registration mail will be sent out as wordpress@your_site with no further intervention.