---- dataentry configoptions ----
type             : constant
name             : MAILQUEUE_THROTTLE
purpose          : Add a delay between messages to avoid overloading the server.
allowed          : Any number, even fractions
default          : 0
status_s         : 
category         : queue processing
----

This is the number of seconds to wait between two messages. You can also use fractions eg 0.5 to wait half a second.