Recipient email rules are criteria enabling you to segment email signatures based on the recipient's email.
For example, you can easily create an email signature for internal emails or segment campaigns for specific companies. 
The order of the rules matters. The first time a rule is met, it stops and does not look for other rules for the same segment. You can sort the order of the rules by dragging the 3 bars with your mouse.
How to create a rule for an internal email signature
How to segment a campaign for external emails
How to segment a campaign to specific recipients
You can segment campaigns to multiple recipients using a semi-colon (there are no spaces before and after the semi-colon).
