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fix: Implement missing "implicit MX" rule

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Implements "implicit MX" as described by
https://datatracker.ietf.org/doc/html/rfc5321#section-5.1

Fixes: #126
Signed-off-by: Jagoda Ślązak <jslazak@jslazak.com>
This commit is contained in:
Jagoda Ślązak
2026-08-18 12:21:28 +02:00
committed by missytake
parent 6121d46234
commit 4131fd0823
1 changed files with 26 additions and 18 deletions
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filtermail/src/transport.rs
+26 -18
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@@ -59,25 +59,33 @@ impl TransportHandler {
allow_invalid_cert = true; allow_invalid_cert = true;
} }
let query = format!("{mx_domain}."); let query = format!("{mx_domain}.");
let mx_records = dns_resolver.mx_lookup(query).await.map_err(|e| {
if e.is_no_records_found() {
format!("512 No MX records for {mx_domain}")
} else if e.is_nx_domain() {
format!("512 Domain {mx_domain} does not exist")
} else {
format!("421 DNS resolution failed for {mx_domain}")
}
})?;
let mut hosts: Vec<(u16, String)> = mx_records match dns_resolver.mx_lookup(query).await {
.iter() Ok(mx_records) => {
.map(|mx| { let mut hosts: Vec<(u16, String)> = mx_records
let host = mx.exchange().to_string().trim_end_matches('.').to_string(); .iter()
(mx.preference(), host) .map(|mx| {
}) let host =
.collect(); mx.exchange().to_string().trim_end_matches('.').to_string();
hosts.sort(); (mx.preference(), host)
hosts })
.collect();
hosts.sort();
hosts
}
Err(e) => {
if e.is_no_records_found() {
// "implicit MX" as described by section 5.1 of RFC5321
// https://datatracker.ietf.org/doc/html/rfc5321#section-5.1
log::debug!("No MX record found, using implicit MX: {mx_domain}");
vec![(0, mx_domain)]
} else if e.is_nx_domain() {
return Err(format!("512 Domain {mx_domain} does not exist"));
} else {
return Err(format!("421 DNS resolution failed for {mx_domain}"));
}
}
}
} }
}; };