On the Internet these days, spam is a big problem so WHMCS comes with spam control filters for trying to reduce the amount of spam you receive. The spam control features will allow you to block email address, and keywords or phrases which appear in either the messages subject or body.
Adding a Blocked Email Address
There are two ways to block an email address from opening tickets. The first is the easiest and that is when viewing a ticket from the email you want to block, simply click the "Block Sender" button next to the ticket openers details.
The second method involves going to Setup > Support > Spam Control and using the Add box there to enter the email you want to block and then submit the form to add it.
Blocking Keywords or Phrases
To setup keywords or phrases which if found in an email will prevent it opening a ticket, go to Setup > Support > Spam Control. You can then enter the words or phrases and choose the place they will be looked for - either the subject or body of the message.
If you use more common email addresses (especially hosting companies) such as support@, contact@ ETC. you will tend to receive more spam due to spammers blindly emailing these addresses on several domains. If you use less common addresses you may find your level of incoming spam reduced. E.G.
Something which you can do outside of WHMCS to help combat the number of spam emails you are receiving is enable SpamAssassin. This is a great tool and does a very good job of picking up most spam using it's rule based system and worldwide database of spam messages. For more information, see http://spamassassin.apache.org/