outbound_throttle

Last updated March 2020

Name

outbound_throttle_messages — limit the rate at which messages are delivered

Synopsis

Outbound_Throttle_Messages = "1"

Outbound_Throttle_Messages = "1/60"

Description

This option allows you to limit the rate at which Momentum will attempt to deliver mail. It can be employed to globally limit throughput or to reduce the rate sent to a particular domain.

If a single integer parameter is provided, Momentum will ensure that no more than the specified number of messages are sent in a given second of time. If a proper fraction parameter is provided, Momentum will limit the number of sent message to the number specified in the numerator over the time window in seconds specified by the denominator. By default this option is not set, indicating an unlimited number of deliveries.

Note

For best results, a throttle in the same scope and with the same values should also be defined using outbound_throttle_connections.

If this option is not set or if is set to 0, there is no limit on the number of messages sent.

Throttles and Fallback

In general, the configuration system works by taking the most specific instance of a given configuration option. Consider the following:

opt = "foo"
a {
  b {
    opt = "bar"
  }

  c {}
}

In this case, we have a notional option called opt specified globally, and within the b stanza. If we look it up globally, we get the value "foo. If we look it up inside the "a stanza, it falls back to global, and we get foo. Within the b stanza, it's explicitly set to bar, and this is the value we receive. Inside the c stanza, no value is set, so we fall back to a. As no value is set there, we fall back to the global foo value. The effective values are shown in the following:

opt = "foo"
a {
 opt = "foo"
 b { opt = "bar" }
 c { opt = "foo" }
}

Throttles work in a similar way, but are treated "by reference" as opposed to "by value." Consider the following configuration:

binding_group "mygroup" {
  Outbound_Throttle_Messages = "10"

  binding "mybinding1" {}

  binding "mybinding2" {}

  domain "mydomain1" {}

}

A single throttle structure is created in the scope of the binding group, mygroup. However, this doesn't mean that you end up with a new throttle in each scope. The fallback behavior of the configuration system for throttles means that a broader scope throttle will apply cumulatively to all subordinate options. In other words, options falling back to a less specific stanza to find a throttle will all affect the throttle together.

In the above configuration the combined scopes mybinding1, mybinding2 and mydomain1 may send 10 messages cumulatively within a 1 second time period. Thus, if 10 messages go out for mybinding1, mybinding2 and mydomain1 will not send out any messages within that second.

The following configuration allows 10 messages per second individually for each scope.

binding_group "mygroup" {
  Outbound_Throttle_Messages = "10"

  binding "mybinding1" {
    Outbound_Throttle_Messages = "10"
  }

  binding "mybinding2" {
    Outbound_Throttle_Messages = "10"
  }

  domain "mydomain1" {
    Outbound_Throttle_Messages = "10"
  }
}