Hi Phill,
I investigated this this morning to make sure it works as I expect, and I did find one bug with the notify admin feature. Previously we used a simple web.config setting to enable this and later we moved it into site settings but in the code that sends the email it was still checking the older web.config setting. I will fix this for the next release but for now you can solve it by setting this to true in Web.config
<add key="NotifyAdminsOnNewUserRegistration" value="true"/>
The verification email to the user for the "Require Email Confirmation" setting in site settings does work correctly for me and the notification to admins works if the above web.config setting is true.
Other than that all I know about email configuration is in the article Email Configuration. Note especially though tat if you have enabled this as true:
<add key="EnableSiteSettingsSmtpSettings" value="true" />
then none of the other SMTP settings in user.config are used, instead they must be entered in Site Settings, and if there is more than one site in the installation it must be set in each site.
Hope that helps,
Joe