Clarification on Registration Email
larsentim278054, Excellent point I should clarify. If you are using the default registration workflow (simple reg > full reg), the email issue will not present. Some people didn't like using the simple reg page and modified the site to go straight to the full registration page. That is the circumstance where the email will not send.
However, the check out email not sending presents in all cases so you will likely want to apply that fix.