On the login page of your Vaultastic domain, click the Forgot Password link.
Provide your Vault Id.
Enter the Captcha text shown to prove that you are not a robot and proceed.
The application will generate a verification code that is sent to your primary email account associated with the Vaultastic id. (For the postmaster user, it is the email id using which the domain was registered).
Access your primary email account and copy the verification code you have received.