It is possible that your user is marked as Bounced in the system. Once the email is marked bounced, it is no longer sent any emails from our system.
To check whether or not a user is Bounced, go to App Setup > Users > All Users and do a search for the user while making sure you have the Bounced tab selected at the top. If the user is Bounced, it would appear like this:
To unmark the user as Bounced, you'd need to edit the profile and uncheck the option that says This email is bounced:
That's all! The user should now start receiving alerts/notifications from Lead Liaison system.