1. Login to your Rediffmail account.
2. Click “Settings” on the top right side of the screen.
3. Click on the “Manage Mail >> Block/Unblock Senders”.
4. Mention the email id you want to blocked.

Similarly if you want to unblock any sender.

1. Login to your Rediffmail account.
2. Click “Settings” on the top right side of the screen.
3. Click on the “Manage Mail >> Block/Unblock Senders”.
4. Here you can see blocked sender, you can click on the crossmark to unblock the sender.