kumomta/docs/reference/kumo/configure_bounce_classifier.md

kumo.configure_bounce_classifier {PARAMS}

Configures the bounce classifier. The purpose of the classifier is to attempt to digest complex and wide-ranging responses into a smaller set of categories to help inform the sender how best to respond and react to a delivery failure.

This function should be called only from inside your init event handler.

!!! The precise set of classifications are not yet finalized so are not reproduced here. They can be found in the BounceClass enum in kumomta/crates/bounce-classify/src/lib.rs

The classifier must be configured with a set of rules files that provide mappings from a set of regular expressions to the available classification codes.

kumo.configure_bounce_classifier will compile the merged set of files and rules into an efficient regex set that can quickly match the rule to the classification code.

Once the classifier has been configured via this function, the logging functions will automatically call into it to populate the bounce_classification field.

kumo.on('init', function()
  kumo.configure_local_logs {
    log_dir = '/var/log/kumomta',
  }
  kumo.configure_bounce_classifier {
    files = {
      '/opt/kumomta/share/bounce_classifier/iana.toml',
    },
  }
end)

The iana.toml file is provided with rules that map from IANA defined status codes to an appropriate bounce class.

You may create and maintain your own classifications and add them to the list of files.

Here's an excerpt of the iana.toml:

# This file contains rules that match SMTP ENHANCEDSTATUSCODES
# codes as defined in the IANA registry:
# https://www.iana.org/assignments/smtp-enhanced-status-codes/smtp-enhanced-status-codes.xhtml
# to bounce classifications.
[rules]
InvalidRecipient = [
  "^(451|550) [45]\\.1\\.[1234] ",
  "^45[02] [45]\\.2\\.4 ", # Mailing list expansion
  "^5\\d{2} [45]\\.7\\.17 ", # RRVS: Mailbox owner has changed
]
BadDomain = [
  "^(451|550) [45]\\.1\\.10 ", # NULL MX
  "^5\\d{2} [45]\\.7\\.18 ", # RRVS: domain owner has changed
]
InactiveMailbox = [
  "^(451|550) [45]\\.1\\.[6] ",
  "^[45]\\d{2} [45]\\.2\\.1 ",
  "^525 [45]\\.7\\.13 ", # User account disabled
]
InvalidSender = [
  "^(451|550) [45]\\.1\\.[78] ",
  "^\\d{3} [45]\\.7\\.27 ", # Send address has NULL MX
]
QuotaIssues = [
  "^552 [45]\\.2\\.2 ",
  "^552 [45]\\.2\\.3 ",
  "^452 [45]\\.3\\.1 ", # Mail System Full
  "^55[24] [45]\\.3\\.4 ", # Message too large for system
]