You can follow the steps in the screenshots to set a Private Key Password.
The enhanced protection level: In order to enhance the private key security, we recommend every user log in MeSince website to set the private key protection password (set a password that is different from the email account password), so that MeSince not only needs to verify the email account when issuing the certificate, at the same time, it also needs to verify the private key password set by the user, which doubles the protection of private key security and encrypted email security.
The advantage is that even if the email account password is stolen or hacked, the thief cannot get the encrypting certificate because the thief does not know the private key password, thus ensuring that the encrypted email will not be stolen; the disadvantage is that the user not only needs to remember the email account password, but also need to remember the private key password, remember one more password. If you need to export the certificate, you need to verify this password. Please note: If your email is already used to bind other service system accounts, it is highly recommended that you use this Enhanced Protection Level, and set a private key password.