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ignore_8bit_checks

Since: Version 2025.10.06-5ec871ab

The functionality described in this section requires version 2025.10.06-5ec871ab of KumoMTA, or a more recent version.

When set to true, the SMTP client will not pre-emptively consider a message send attempt as a permanent failure when it would require either 8BITMIME or SMTPUTF8 support to be advertised by the next hop and the next hop does not advertise the appropriate extension.

The default behavior (when this is set to false) is to consider the message content and the message envelope.

If the content is 8bit and 8BITMIME is not advertised by the next hop, the message is not deliverable according to the various SMTP RFCs. The resolution to this issue is, in order of preference:

  1. Ensure that the generator of the message is using appropriate transfer encoding.
  2. Deploy a policy that uses msg:check_fix_conformance during reception to rewrite the message (likely breaking any digital signatures in the incoming message).

If the envelope is 8bit and SMTPUTF8 is not advertised by the next hop, then there is no way to deliver that message to that destination. The only way to successfully deliver such a message (assuming that the recipient is actually valid) is to ensure that you have configured routing to deliver directly to the recipient providers domain (eg: don't route via a smart host that doesn't support SMTPUTF8).

kumo.on('get_egress_path_config', function(domain, source_name, site_name)
  return kumo.make_egress_path {
    ignore_8bit_checks = false,
  }
end)