For over a year now, there have been frequent issues with Wikidot account creation failing to send confirmation emails, but recently this issue seems to have increased in frequency and a former workaround where using the create with facebook option would always work no longer does. This does not occur only with email addresses from forbidden domains, and it has happened to users trying multiple times with multiple valid email addresses.
This is still ongoing, and is affecting users trying to join Wikidot worldwide.