You can block unwanted email according to email address, subject, header, recipient, or even phrases inside the body of the message.
To block unwanted email:
Click on Block an Email
Click on Add Filter.
Use the drop down menus to choose what you want blocked. For example, you might want to filter out pornographic email messages. You could choose Subject, Body or Any Header from the first drop down menu, and Contains from the second drop down menu. Then type a phrase or word that frequently appears in the header or body of email you receive that promotes pornographic content, For example "girls." To block email from a specific source, just choose From in the first drop down menu, then Equals from the second menu. Type in the person's email address in the box and click Activate.
It is not the account that should be disabled for sending email, it is the ip address which typically needs to be disabled from sending emails using your SMTP server (as long as you have enabled relaying). If you are looking at blocking his domain altogether, I'd suggest enable rbl and include his local domain in the blacklist. A search on the technical and security tutorials will give you details about setting up rbl.
SupportExpertz.com - the name says it all!
Managed Cloud Servers
Server Management and Monitoring
24x7 outsourced customer support