I sort of fixed this by accident! I went into the global settings of the main joomla site, changed the mailer settings to PHP-Mailer and re-entered my e-mail address in 'Mail From'. I though I had previously tired this but it worked this time!
Thanks for the reply. I tried that too but unfortunately it hasn't sovled the problem for me. I've even gone through and done a complete reinstall of CB. I'm stumped.
My site is sending mail fine, as I can receive e-mails sent out by my contact forms. It's just the CB registration activation e-mails that never show up.
Been trying to solve this problem for about two weeks straight now.