There are multiple possible reasons that a Rediff mail inbox cannot be opened, including login issues, valid session issues, and password issues. Some issues may require direct contact with Rediff to resolve.
If the user is unable to login to his account, he needs to click on the link named "Forgot Your Password?" Next, he must enter his username, click submit and provide necessary details about birthday and residence location. The final step is answering the hint question, after which a new password will be displayed for the user.
If the user cannot remember the answer to the Hint Question, he will need to click the "No, Contact Customer Care" button on Rediff's support site. This lets the user send a message to Rediff, and Rediff will then provide the password to the alternate email address provided when the user first signed up for Rediff.
If the user receives a message about the session being invalid, the session has expired after thirty minutes of nothing being clicked. The user will need to login again to resume the session. Rediff recommends using the Save Draft feature when composing longer emails so that they are not lost due to expired sessions. Rediff recommends ensuring that the browser's per-session cookie feature is enabled to avoid problems with invalid sessions.