In fact, you can have a farm of Brightmail servers serving one or more MTAs.
The Brightmail server is deployed at a customer site.
Brightmail has email probes set around the Internet for detection of new spam.
There can be multiple lines of this attribute specifying several domains which are all considered local.
Local versus foreign domain is used to specify two different handling for a verdict.
A false-positive results when Brightmail believes that a message is spam when it in fact is not spam.