The Recipient Number criteria allows you to create rules that take actions on messages based on the number of recipients the message is addressed to.
The Attachment is "password protected" and Recipient number criteria become available.
Select > to apply the rule to messages that are sent to more than the specified number of recipients.
Select <= to apply the rule to messages that have the same number or fewer than the specified number of recipients.
For example:
> 10 applies the rule to all messages that have more than 10 recipients.
<= 10 applies the rule to all messages that have 10 or fewer recipients.