You would like to setup a Content Filtering policy on a Symantec Messaging Gateway (SMG) to only allow outbound mail where the FROM address belongs to 1 or more domains.
Such a policy would be helpful in preventing trusted users/hosts, from sending Outbound Emails where the FROM address in the message does not match a set list of domains.
The following policy configuration can be used in enforcing this requirement with Outbound mail.
1/ Create a Dictionary featuring all domain names you wish to accept Email from (this might include your own domains)
2/ Create a Content Filtering policy with the following details selected:
Apply to: Outbound messages
Which of the following conditions must be met: Any
Condition: If text in the Envelope sender part of the message header does not contain Domain name from dictionary "Select Domain name list"
Actions: here you can specify which action you wish to apply to not accept the message, such as "Send a bounce message"