This is a global setting for a listener (Inbound or Outbound). There is no way to define exceptions or have some sender override it based on any policy. The default value is 1024 and there is no limit imposed by the Control Center on high you can set. You should set it to the number that you want to allow for your outbound mail. But it's not a good idea to increase the value for Inbound listener
If you are using Exchange, I think limiting the number of recipients per message before it leaves exchange is a better way to avoid any issues with outbound mail.
Regards,
Adnan