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Dns_trie.check maybe too strict #412

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#413
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Dns_trie.check maybe too strict#412
#413
@reynir

Description

@reynir
reynir
opened on Feb 25, 2026

In Dns_trie.check we check MX records pointing to a subdomain that the subdomain has an address:

ocaml-dns/server/dns_trie.ml

Lines 305 to 318 in facec28

| B (Mx, (ttl, mxs)) ->
if ttl < 0l then
Error (`Bad_ttl (name, v))
else if Rr_map.Mx_set.is_empty mxs then
Error (`Empty (name, K Mx))
else
let domain = match state' with `None -> name | `Soa zone -> zone in
Rr_map.Mx_set.fold (fun { mail_exchange ; _ } r ->
let* () = r in
if Domain_name.is_subdomain ~subdomain:mail_exchange ~domain then
guard (has_address mail_exchange) (`Missing_address mail_exchange)
else
Ok ())
mxs (Ok ())

This prevents mistakes adding MX records that cannot be delivered mail to. However, I don't think this should be a fatal error, and the domain might even have additional MX records some of which do have addresses making mail delivery possible (although not quite optimal). So maybe this can be promoted to a warning instead?

See also
robur-coop/dns-primary-git#29

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