Hi,
If the goal here is to block spam, do consider that spam is sent from distributed botnets all over the world - check out
www.symantec.com/spam for the latest State of Spam report detailing the top 10 countries where spam is originating from. The Symantec anti-spam products would already use extensive reputation filters to block known spammy IPs.
A safer method might be to block messages in undesired languages, depending on the specific product being used this may already be possible in your product.
Amanda