Registration emails not being sent

Hi there

I am in the process of developing an eCommerce site. (Its not live yet so I cant send a link) but I seem to be having a problem with my registration email. When I register on the site as a customer it says an email with a password will be sent to me but I havent received this email. I have tried this 3 times now with different email addresses but have had no success.

ANY help would be great! Thanks