Inbound spam filtering is now commonplace. Outbound spam filtering isn't; but it should be.
If a PC in your organization gets infected with malware -- such as a remote-access Trojan -- it may become a spam zombie. This means that it will send spam under the remote control of a spammer. This can happen despite your best efforts with firewalls and anti-virus technology.
If the recipients of the spam track down the source of these spam messages, they won't reach the spammer -- they'll reach you. Your organization is therefore at risk of abuse complaints to your ISP or spam blacklisting, either of which can have serious consequences for your business operations. Outbound spam filtering can help prevent this from happening.
Tags: spam, virus, malware.