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Wez Furlong 38fd692e94 docs: show how to skip IPv6

I was halfway through adding special purpose options for this,
but I realized that skip_hosts already exists for this function
and is much more flexible.

Add an example to the docs to show how it can be done.
The same technique can be used to skip using IPv4 if that is
desired (despite being impractical with the current state
of SMTP on ipv6), but using `0.0.0.0/0` as an entry in the
skip_hosts list.

closes: https://github.com/KumoCorp/kumomta/issues/317

2024-12-04 07:33:50 -07:00

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skip_hosts

A CIDR list of hosts that should be removed from the list of hosts returned when resolving the MX for the destination domain.

This can be used for example to skip a host that is experiencing issues.

If all of the hosts returned for an MX are filtered out by skip_hosts then the ready queue will be immediately failed with a 550 5.4.4 status.

Skipping IPv6 Addresses

When performing MX resolution, KumoMTA will always resolve both the IPv4 and IPv6 addresses as part of its connection plan. If your infrastructure cannot or for policy reasons, should not use IPv6 you can set:

kumo.make_egress_path {
  -- Don't use IPv6 for deliveries
  skip_hosts = { '::/0' },
}

If you are using the shaping helper, you can express that in your shaping.toml:

[default]
skip_hosts = ["::/0"]

830 B Raw Blame History

skip_hosts

Skipping IPv6 Addresses

830 B

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