I had the same problem and contacted the Plusnet support desk. For the past week, my emails have declined from 10 to 20 per day to less than 6 in a week. I also watched some emails vanish from the Inbox in Webmail. They suggested that I change my password as the only way this could be happening is if an unauthorised email client is downloading the emails from the server. I changed my password and solved my problem. It will take about 30 minutes for any changes to your email password to take place. I would also recommend that your password be 8 characters long and a mixture of letters and numbers as this will be harder for any miscreants to crack (my original password was 7 characters long and all letters).