Commit 8fab350b authored by Alberto Bertogli's avatar Alberto Bertogli

courier: DNS temporary errors should cause temporary delivery failures

In the SMTP courier, when the MX lookup fails with a DNS temporary
error, we should propagate that up and cause delivery to fail with a
temporary error too.

That way the delivery can be attempted later by the queue.

However, the code today doesn't make the distinction and will treat any
temporary DNS error as a permanent delivery failure, which is a bug.

The bug was found by ludusrusso and reported in
https://github.com/albertito/chasquid/issues/4

This patch fixes the bug by propagating the error properly.
parent 6641d858
Pipeline #127727471 passed with stages
in 8 minutes and 50 seconds
......@@ -68,13 +68,13 @@ func (s *SMTP) Deliver(from string, to string, data []byte) (error, bool) {
a.from = ""
}
mxs, err := lookupMXs(a.tr, a.toDomain)
mxs, err, perm := lookupMXs(a.tr, a.toDomain)
if err != nil || len(mxs) == 0 {
// Note this is considered a permanent error.
// This is in line with what other servers (Exim) do. However, the
// downside is that temporary DNS issues can affect delivery, so we
// have to make sure we try hard enough on the lookup above.
return a.tr.Errorf("Could not find mail server: %v", err), true
return a.tr.Errorf("Could not find mail server: %v", err), perm
}
// Issue an EHLO with a valid domain; otherwise, some servers like postfix
......@@ -245,10 +245,10 @@ func (s *SMTP) fetchSTSPolicy(tr *trace.Trace, domain string) *sts.Policy {
return policy
}
func lookupMXs(tr *trace.Trace, domain string) ([]string, error) {
func lookupMXs(tr *trace.Trace, domain string) ([]string, error, bool) {
domain, err := idna.ToASCII(domain)
if err != nil {
return nil, err
return nil, err, true
}
mxs := []string{}
......@@ -264,10 +264,10 @@ func lookupMXs(tr *trace.Trace, domain string) ([]string, error) {
dnsErr, ok := err.(*net.DNSError)
if !ok {
tr.Debugf("MX lookup error: %v", err)
return nil, err
return nil, err, true
} else if dnsErr.Temporary() {
tr.Debugf("temporary DNS error: %v", dnsErr)
return nil, err
return nil, err, false
}
// Permanent error, we assume MX does not exist and fall back to A.
......@@ -292,5 +292,5 @@ func lookupMXs(tr *trace.Trace, domain string) ([]string, error) {
}
tr.Debugf("MXs: %v", mxs)
return mxs, nil
return mxs, nil, true
}
......@@ -213,10 +213,13 @@ func TestTooManyMX(t *testing.T) {
{Host: "h3", Pref: 30}, {Host: "h4", Pref: 40},
{Host: "h5", Pref: 50}, {Host: "h5", Pref: 60},
}
mxs, err := lookupMXs(tr, "domain")
mxs, err, perm := lookupMXs(tr, "domain")
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
if perm != true {
t.Fatalf("expected perm == true")
}
if len(mxs) != 5 {
t.Errorf("expected len(mxs) == 5, got: %v", mxs)
}
......@@ -230,10 +233,13 @@ func TestFallbackToA(t *testing.T) {
IsTemporary: false,
}
mxs, err := lookupMXs(tr, "domain")
mxs, err, perm := lookupMXs(tr, "domain")
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
if perm != true {
t.Fatalf("expected perm == true")
}
if !(len(mxs) == 1 && mxs[0] == "domain") {
t.Errorf("expected mxs == [domain], got: %v", mxs)
}
......@@ -247,10 +253,13 @@ func TestTemporaryDNSerror(t *testing.T) {
IsTemporary: true,
}
mxs, err := lookupMXs(tr, "domain")
mxs, err, perm := lookupMXs(tr, "domain")
if !(mxs == nil && err == testMXErr["domain"]) {
t.Errorf("expected mxs == nil, err == test error, got: %v, %v", mxs, err)
}
if perm != false {
t.Errorf("expected perm == false")
}
}
func TestMXLookupError(t *testing.T) {
......@@ -258,19 +267,25 @@ func TestMXLookupError(t *testing.T) {
testMX["domain"] = nil
testMXErr["domain"] = fmt.Errorf("test error")
mxs, err := lookupMXs(tr, "domain")
mxs, err, perm := lookupMXs(tr, "domain")
if !(mxs == nil && err == testMXErr["domain"]) {
t.Errorf("expected mxs == nil, err == test error, got: %v, %v", mxs, err)
}
if perm != true {
t.Fatalf("expected perm == true")
}
}
func TestLookupInvalidDomain(t *testing.T) {
tr := trace.New("test", "test")
mxs, err := lookupMXs(tr, invalidDomain)
mxs, err, perm := lookupMXs(tr, invalidDomain)
if !(mxs == nil && err != nil) {
t.Errorf("expected err != nil, got: %v, %v", mxs, err)
}
if perm != true {
t.Fatalf("expected perm == true")
}
}
// TODO: Test STARTTLS negotiation.
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