Ok, looks like the issue is with our SPF, DKIM, and DMARC records. So, it's affecting all notifications. Had them reapplied but it can take 12 to 48 hrs for them to promulgate and start working again.
Gmail accounts are currently blocking email notifications sent to them from the SFF forum. So, if you register or change your e-mail to it PM me on the forum or let me know here. Give your username and I'll approve the accounts.
Just a follow up but there's been a change to the login procedure now. Before you could just login with your display name but after the update you'll have to use the current e-mail address for your account.