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PMTA knowledge base›Mechanism§ 11.5

Reputation monitoring inside the node

critical

sender reputation monitoring
The engine notices deterioration itself and responds

Reputation monitoring built into the node: receiving servers’ replies are matched against expressions, and on a match the queue goes into backoff mode.

Its value is speed. The engine responds in the same connection where it saw the refusal; an outside observer learns from telemetry minutes later.

The main trap is waiting for a notification without an address. The switch to backoff mode is silent by itself: a message about it goes out only if backoff-notify is set, otherwise people find out from the growing queue.
What the Hub does. It uses it: the policy template attaches the smtp-pattern-list blocking-errors list to receiver blocks — expressions over reply texts with mode=backoff — and the presets set the behavior in backoff mode: backoff-max-msg-rate, backoff-retry-after and rerouting to a reserve address with backoff-reroute-to-virtual-mta. On top of that the Hub collects backoff episodes every five minutes and applies its own policies.
Recommended values

What a queue does in backoff mode:

Action Directive
sends a notification backoff-notify
changes the retry schedule backoff-retry-after
lowers the rate backoff-max-msg-rate
moves messages to another sending address backoff-reroute-to-virtual-mta
Queue modes, the four actions and the link to the expression list come from the manual (§ 11.5). The trap analysis is ours.
Example configuration
<smtp-pattern-list aol-errors>
    reply /421 .* too many errors/ mode=backoff</smtp-pattern-list>
<domain aol.com>
    smtp-pattern-list aol-errors
    backoff-max-msg-rate 120/h
    backoff-retry-after 1h
</domain>
A shortened example from the manual: a matching reply puts the queue into backoff mode, and the receiver block sets what to do in it.
yellow — — directive names, blue — blocks. They are highlighted the same way in the text of the card.
Compatibility
PowerMTA 6.0
described in the manual of this version · platform: any
The vendor does not state the first version for every directive — there is no note here. The name also appears in the 5.0 edition of the manual.
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Related entries

4 relations

Does not work without

How the node responds to the receiving server's wordsA related mechanism: they work together. § 11.5.2

Works together with

Change a queue's mode by handThe command through which the mechanism is observed. § 11.5.3

Affects

backoff-reroute-to-virtual-mta<domain>The directive that enables this mechanism. § 11.5.2

Where you can see it

Backoff mode — the queue's second personalityA related mechanism: they work together. § 11.5.2

Referenced from

Recipient eventsA related mechanism: they work together. inferenceSpreading a stuck queue across several addressesRerouting is the strongest reaction to worsening reputation; this form of it changes its meaning from retreat to dispersal. § 11.18.1

How to check on the node
See which queues are in backoff mode and why:
pmta show queues --mode=backoff --errors --no-rcpt-events --maxitems=1000
The last error on each queue is the reply that matched the expression.
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What else to read

3 articles

◇How the policy for a receiver is assembledSettings are assembled from the most general pattern to the most precise; the order of blocks in the file means nothing.◇Backoff mode — the queue's second personalityA queue that a receiver has started refusing switches to a parallel set of limits, retries and routes — ten directives that act only in this mode.◇Recipient eventsThe last 50 delivery, bounce and deferral events per queue — enabled with track-recipient-events and visible in queue output.

In the Hub
Cost of a mistake
reversible: harms only while it is set
Scenarios
Troubleshoot deliverability · Tune the pace for a provider
Priority
critical