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delay_dsn – Delay DSN Generation

Last updated March 2020

The delay_dsn module allows delivery status notifications (DSNs) to be sent to the purported sender of a message, when that message has not yet been delivered.

By default, no delay DSNs are sent. When enabled, delay DSNs are sent based on an exponential back-off schedule. The schedule is independent of the schedule used for delivery attempts. Delay DSNs are sent as RFC 3464-compliant messages.


Sending of delay DSNs and the schedules can be configured in various scopes. If further customization is required, there are a number of hooks available. These hooks can be used to achieve: different types of schedules, such as every N hours instead of exponential back-off; customization of the message content; and finer-grained control over to who delay DSNs are sent.

The following is an example configuration:

delay_dsn "delay_dsn1" { }

generate_delay_dsn = "true"

# don't generate delay dsns for mail from
domain "" {
  generate_delay_dsn = "false"

domain "" {
  # custom delay dsn schedule. send a delay dsn on 3 hours, then 9 hours
  # (6 hours after 3 hours), 21 hours (12 hours after 9 hours),
  # 45 hours (24 hours after 21 hours), then every 24 hours
  # (maximum interval).
  delay_dsn_retry_interval = 10800
  delay_dsn_max_retry_interval = 86400

Console Commands

The delay_dsn module can be controlled through the ec_console. The following command is available:

delay_dsn:*`delay_dsn1`* show pending events

This command lists all pending events.

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