To filter Internet Email, Microsoft Exchange Server users can create a rule that looks like this:
Apply this rule after the message arrives
with @ in the sender's address
<whatever actions you want>
except with @mycompany.com in the sender's address
This is a client-only rule, because the "with specified words in the sender's address" condition is an Outlook-only condition that does not have an analog in the conditions used by the Exchange Server to process rules.
This rule works because email sent through the Microsoft Exchange service does not have a header and Exchange server addresses do not contain the @ symbol. The exception is not needed for mail originating inside the company but is added to capture mail sent using other services that use a SMTP server as well as messages sent by some smartphone configurations.
If you don't use an Exchange server, your rule would read exactly as above or you could look for @mycompany.com in the sender's address and act on it.
Do you want to filter messages sent by other users of your Exchange server? Use /ou as the words in the address.
Search Folder Criteria
If you prefer to use a Search Folder, choose the predefined Search folder for Mail from Specific People .
Click Choose, then type @ in the From field and click Ok.