smtp functionality appears to have started failing

Hi, My new users who register on my xwiki site appear to not be able to recieve email consfirmations on registraiton. I'm using the latest stable release and have discovered that smtp (for email registration) appears to have stopped working. It did work previously with customized RegisterNewUser and RegisterNewUserConfirmation pages. To rule out my customizations, I copied and pasted the version on xwiki and this did not help. How do I start troubleshooting this? Regards, Dennis