A user, bvdrie72, reports that after migrating to SSO, 9 email addresses are failing with the error “Validation failed: Primary email is not allowed.” Despite the emails being valid and not existing in Discourse, they are being blocked. Stephen suggests investigating commonalities in the email addresses, such as length or characters. bvdrie72 notes no clear pattern, with most being Gmail accounts and using alphanumeric characters. codinghorror advises checking the “Screened Emails” list in Admin, Logs. bvdrie72 confirms the issue was resolved by approving the emails in the screened list, resolving the SSO error.
Check your blocked emails in Admin, Logs, Screened Emails. And remember emails that are too close to the blocked emails (such as superdave versus superdave1) will also be blocked.