When you are on SSH you can simply run as root plesk login
to see a "secret" login link that you can copy-paste to the browser. Or you can add a username as a second parameter so that you get that login link for the user. It is not necessary to receive it by email.
If you do not receive the link by email, please check /var/log/maillog what happens with the email that the server generates, e.g whether it is sent, to where it is sent and what the result is.