
39vec (39vec) asked a question.
We have the exact same thing as this thread :
Newly imported users are not getting an activation email. All spam folders, filters, settings, etc have been ruled out as the cause. Recipient email addresses are all @codecorp.com .
Without this email the user gets the generic "Unable To Sign In" error immediately after entering username. Doesn't even get to the password prompt. If I manually activate their account the error still occurs. So I'm stuck since the link in the activation email seems to be the only way to get them in.

Thank you for posting your question.
Please feel free to open a case with Okta in order to see what is the exact issue with @codecorp.com .