No. The MailScanner Front-End service is designed to protect your server
and your users from incoming spam only. If you think someone is using
your server to send out spam emails, there are many better ways to detect and prevent outgoing spam. Some suggestions:
1) Use a malware detection system such as cxs (ConfigServer eXploit Scanner) to detect exploits that may be used for sending spam, and check any reported files and remove them if necessary.
2) Configure relay tracking in csf, monitor the alerts that are sent when the relay limit is exceeded, and check the reported accounts for vulnerable scripts.
3) If you can get the header of one of the outgoing spams, search the exim log to find out what script is sending the mail.
4) Check this webpage on our site which gives some suggestions for finding spammers on your server:http://www.configserver.com/free/spammers.html#outbound
5) Set WHM > Tweak Settings > Mail > Max hourly emails per domain to a low figure such as 100 to ensure that thousands of messages are not sent out before you detect it.
You may be interested in the cPanel Service Package
which includes installation of cxs and csf which are mentioned above.