After all the work on the Postfix queue scheduler in the past weeks,
this was the only opportunity in the forseeable future to add
support for output rate control, so I did it in a few lines, and
at the same time took the opportunity to clean up some code.
Major changes with Postfix snapshot 20071202
Output rate control in the queue manager. For example, specify
"smtp_delivery_rate_delay = 5m", to pause five minutes between
message deliveries. More information in the postconf(5) manual
postconf(5) man page:
default_delivery_rate_delay (default: 0s)
The default amount of delay that is inserted between individual deliv-
eries to the same destination; with per-destination recipient limit >
1, a destination is a domain, otherwise it is a recipient.
To enable the delay, specify a non-zero time value (an integral value
plus an optional one-letter suffix that specifies the time unit).
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
NOTE: the delay is enforced by the queue manager. The delay timer state
does not survive "postfix reload" or "postfix stop".
Use transport_delivery_rate_delay to specify a transport-specific over-
ride, where transport is the master.cf name of the message delivery
This feature is available in Postfix 2.5 and later.