Hi JanJan,

We've just tested on your website and receive the email notification. 

Sometimes the confirmation email goes to spam-box and users don't check it. The users should check in spam-box as well.

Thank you for your swift reply. We have also had many user registrations without any issues, sometimes they found the confirmation in the junk folder but other times, the email notification just doesn´t arrive. One user did not remember that he had signed up previously and when he tried to reset his password, no email was received to do so (checked spam box). We then deleted the user to have him do a fresh registration, after which  no email to reset the password ever arrived. We then tried to do a registration on his behalf but the confirmation email did not arrive in his inbox/spam. When we tested on our side with yet another of our email accounts, the email got received, so it is hard to replicate his experience consistently. We´d love to give him a solution asap.

Emails, login and registrations belong to Wordpress and not wpForo.

To debug this, install some plugin ( https://wordpress.org/plugins/post-smtp/ for example) enable and check the logs of the email transcations.