source_selection_rate

Since: Dev Builds Only

The functionality described in this section requires a dev build of KumoMTA. You can obtain a dev build by following the instructions in the Installation section.

Optional throttle spec string.

Specifies the maximum permitted rate at which the source that is associated with this egress path can be selected during the promotion of a message from the scheduled queue to the ready queue of this egress path.

This option can be used to help manage IP-warmup.

For example, if you have two sources in a pool named mypool:

new - a new source that you want to use sparingly until you have established a good reputation for it
established - a source that is fully established

And you have a shaping.toml configuration like:

["example.com".sources."new"]
# You will probably want to set max_burst for this sort of throttle,
# to avoid clumping all the sends together at the start of the day
source_selection_rate = "100/day,max_burst=1"

and a queue.toml configuration like:

[queue.'example.com']
egress_pool = 'mypool'

then messages destined for example.com will use the regular weighted round-robin source selection from mypool, but it will be modified slightly:

Whenever the new source is selected by the weighted round-robin algorithm, source_selection_rate (and additional_source_selection_rates) will be consulted to see if there are rate limits for selection.
If any selection rate limits are present, the throttles are sorted from smallest to largest and then checked
If there is remaining capacity in the throttles then the source will be selected.
The first limit that is exceeded will cause the source to be ineligible for this particular selection, and the round-robin algorithm will proceed to try the next potential candidate source