Drupal Auction module - Mails not send
Did you look at Debugging your Email on a development server? Have you looked at the Rules module and the Auction Rules to see if their firing (it sounds like they are)? Did you create hook_mail_alter() to see what email drupal thinks it's sending?

Does your "Create Account" email message fully validate as an email sent from a valid domain, etc.

It's email -- there are no easy answers :)