How do throttles in different scopes interact?

The standard precedence for throttles (and limits, as well) is as follows, from less specific to more specific:

Global -> Domain -> Binding Group -> Domain -> Binding - > Domain

This means that a setting in a precedence level will override the same setting in any precedence levels to its left; settings in the global scope are always overridden by the same setting in any other precedence level.

N.B. this is not applicable at this level to Adaptive Delivery.

Using throttles as an example, ecelerity.conf could contain the following:

Outbound_Throttle_Messages="10/5"

domain "fakedomain.com" {
    Outbound_Throttle_Messages="1/5"
}

binding "test" {
    domain "fakedomain.com" {
        Outbound_Throttle_Messages="5/5"
 }

In this example, the domain fakedomain.com will have an Outbound_Throttle_Messages setting of 1/5 unless it is going out the binding "test", when it will increase to 5/5. The global setting of 10/5 will always be overridden for fakedomain.com. All other domains will use the global setting of 10/5.