delay all outbound mail

[jeffs]

I need to delay all outbound email, not specific to destination 
domains.  I have tried to make the smtp_destination_rate_delay = 180

but I believe that must work in conjunction with specific domains 
(please someone tell me if that is the case because the documentation, 
although it says one should specify the delayed to domain, doesn't 
specify that this MUST be the case).

What would be the best way to delay ALL outbound email?

Thanks in advance