What does [GBS] in an Email Subject Mean?

When an email originates or is relayed from an IP that is listed on Symantec's Global Bad Sender list, the subject of the email is prepended with [GBS]. The Symantec Global Bad Sender list is a list of IP addresses collected by Symantec, based on global spam data from mail servers protected by Symantec.

Redtail utilizes Symantec as our email gateway. Mail is scanned by Symantec for viruses and other malicious content then passed on to SpamAssassin to be scanned as part of Redtail's multi-layered spam detection process.