Thanks for your posting. TestRail also generated strong, random passwords for the new user accounts in this case. Since you’ve disabled the Invite option, the passwords weren’t sent to the users and the user accounts are effectively “disabled” in this case if you will.
The idea in this case is to manually send the new users an email with a link to the Login/Forgot Password form so that the users can generate a new password on this page. You can alternatively integrate TestRail with SSO (single-sign-on) systems such as LDAP or Active Directory and you can find the details here:
I hope this helps and please let me know in case you have any further questions!