For the last 2/3 days registering users have not received their activation emails even though there are no errors in the error log and the user is appearing in the inactive user list. Any ideas why this might be? Do not think it is a board problem as nothing has changed, it is either a hosting problem or a "blacklist" problem.
In addition to the link above, test your email domain to see if it has been placed on a blacklist. If true, then you'll need to contact your hosting company if you use their email services or the company of which you use email from.