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aliases: Implement "via" aliases

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This patch implements "via" aliases, which let us explicitly select a
server to use for delivery.

This feature is useful in different scenarios, such as a secondary MX
server that forwards all incoming email to a primary.

For now, it is experimental and the syntax and semantics are subject to
change.
This commit is contained in:
Alberto Bertogli
2025-04-06 12:35:51 +01:00
parent 1cf24ba94a
commit 9999a69086
28 changed files with 671 additions and 74 deletions
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54
internal/queue/queue.go
View File

@@ -191,6 +191,9 @@ func (q *Queue) Put(tr *trace.Trace, from string, to []string, data []byte) (str
r.Type = Recipient_EMAIL
case aliases.PIPE:
r.Type = Recipient_PIPE
case aliases.FORWARD:
r.Type = Recipient_FORWARD
r.Via = aliasRcpt.Via
default:
log.Errorf("unknown alias type %v when resolving %q",
aliasRcpt.Type, t)
@@ -387,6 +390,21 @@ func (item *Item) deliver(q *Queue, rcpt *Recipient) (err error, permanent bool)
return cmd.Run(), true
}
// Recipient type is FORWARD: we always use the remote courier, and pass
// the list of servers that was given to us.
if rcpt.Type == Recipient_FORWARD {
deliverAttempts.Add("forward", 1)
// When forwarding with an explicit list of servers, we use SRS if
// we're sending from a non-local domain (regardless of the
// destination).
from := item.From
if !envelope.DomainIn(item.From, q.localDomains) {
from = rewriteSender(item.From, rcpt.OriginalAddress)
}
return q.remoteC.Forward(from, rcpt.Address, item.Data, rcpt.Via)
}
// Recipient type is EMAIL.
if envelope.DomainIn(rcpt.Address, q.localDomains) {
deliverAttempts.Add("email:local", 1)
@@ -396,24 +414,32 @@ func (item *Item) deliver(q *Queue, rcpt *Recipient) (err error, permanent bool)
deliverAttempts.Add("email:remote", 1)
from := item.From
if !envelope.DomainIn(item.From, q.localDomains) {
// We're sending from a non-local to a non-local. This should
// happen only when there's an alias to forward email to a
// non-local domain. In this case, using the original From is
// problematic, as we may not be an authorized sender for this.
// Some MTAs (like Exim) will do it anyway, others (like
// gmail) will construct a special address based on the
// original address. We go with the latter.
// Note this assumes "+" is an alias suffix separator.
// We use the IDNA version of the domain if possible, because
// we can't know if the other side will support SMTPUTF8.
from = fmt.Sprintf("%s+fwd_from=%s@%s",
envelope.UserOf(rcpt.OriginalAddress),
strings.Replace(from, "@", "=", -1),
mustIDNAToASCII(envelope.DomainOf(rcpt.OriginalAddress)))
// We're sending from a non-local to a non-local, need to do SRS.
from = rewriteSender(item.From, rcpt.OriginalAddress)
}
return q.remoteC.Deliver(from, rcpt.Address, item.Data)
}
func rewriteSender(from, originalAddr string) string {
// Apply a send-only Sender Rewriting Scheme (SRS).
// This is used when we are sending from a (potentially) non-local domain,
// to a non-local domain.
// This should happen only when there's an alias to forward email to a
// non-local domain (either a normal "email" alias with a remote
// destination, or a "forward" alias with a list of servers).
// In this case, using the original From is problematic, as we may not be
// an authorized sender for this.
// To do this, we use a sender rewriting scheme, similar to what other
// MTAs do (e.g. gmail or postfix).
// Note this assumes "+" is an alias suffix separator.
// We use the IDNA version of the domain if possible, because
// we can't know if the other side will support SMTPUTF8.
return fmt.Sprintf("%s+fwd_from=%s@%s",
envelope.UserOf(originalAddr),
strings.Replace(from, "@", "=", -1),
mustIDNAToASCII(envelope.DomainOf(originalAddr)))
}
// countRcpt counts how many recipients are in the given status.
func (item *Item) countRcpt(statuses ...Recipient_Status) int {
c := 0

49
internal/queue/queue.pb.go
View File

@@ -23,8 +23,9 @@ const (
type Recipient_Type int32
const (
Recipient_EMAIL Recipient_Type = 0
Recipient_PIPE Recipient_Type = 1
Recipient_EMAIL Recipient_Type = 0
Recipient_PIPE Recipient_Type = 1
Recipient_FORWARD Recipient_Type = 2
)
// Enum value maps for Recipient_Type.
@@ -32,10 +33,12 @@ var (
Recipient_Type_name = map[int32]string{
0: "EMAIL",
1: "PIPE",
2: "FORWARD",
}
Recipient_Type_value = map[string]int32{
"EMAIL": 0,
"PIPE": 1,
"EMAIL": 0,
"PIPE": 1,
"FORWARD": 2,
}
)
@@ -221,6 +224,8 @@ type Recipient struct {
// This is before expanding aliases and only used in very particular
// cases.
OriginalAddress string `protobuf:"bytes,5,opt,name=original_address,json=originalAddress,proto3" json:"original_address,omitempty"`
// The list of servers to use, for recipients of type == FORWARD.
Via []string `protobuf:"bytes,6,rep,name=via,proto3" json:"via,omitempty"`
}
func (x *Recipient) Reset() {
@@ -290,6 +295,13 @@ func (x *Recipient) GetOriginalAddress() string {
return ""
}
func (x *Recipient) GetVia() []string {
if x != nil {
return x.Via
}
return nil
}
// Timestamp representation, for convenience.
// We used to use the well-known type, but the dependency makes packaging much
// more convoluted and adds very little value, so we now just include it here.
@@ -365,7 +377,7 @@ var file_queue_proto_rawDesc = []byte{
0x0a, 0x0d, 0x63, 0x72, 0x65, 0x61, 0x74, 0x65, 0x64, 0x5f, 0x61, 0x74, 0x5f, 0x74, 0x73, 0x18,
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@@ -379,19 +391,20 @@ var file_queue_proto_rawDesc = []byte{
0x75, 0x72, 0x65, 0x4d, 0x65, 0x73, 0x73, 0x61, 0x67, 0x65, 0x12, 0x29, 0x0a, 0x10, 0x6f, 0x72,
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}
var (

4
internal/queue/queue.proto
View File

@@ -27,6 +27,7 @@ message Recipient {
enum Type {
EMAIL = 0;
PIPE = 1;
FORWARD = 2;
}
Type type = 2;
@@ -43,6 +44,9 @@ message Recipient {
// This is before expanding aliases and only used in very particular
// cases.
string original_address = 5;
// The list of servers to use, for recipients of type == FORWARD.
repeated string via = 6;
}
// Timestamp representation, for convenience.

48
internal/queue/queue_test.go
View File

@@ -127,28 +127,52 @@ func TestAliases(t *testing.T) {
defer tr.Finish()
q.aliases.AddDomain("loco")
q.aliases.AddAliasForTesting("ab@loco", "pq@loco", aliases.EMAIL)
q.aliases.AddAliasForTesting("ab@loco", "rs@loco", aliases.EMAIL)
q.aliases.AddAliasForTesting("cd@loco", "ata@hualpa", aliases.EMAIL)
q.aliases.AddAliasForTesting("ab@loco", "pq@loco", nil, aliases.EMAIL)
q.aliases.AddAliasForTesting("ab@loco", "rs@loco", nil, aliases.EMAIL)
q.aliases.AddAliasForTesting("cd@loco", "ata@hualpa", nil, aliases.EMAIL)
q.aliases.AddAliasForTesting(
"fwd@loco", "fwd@loco", []string{"server"}, aliases.FORWARD)
q.aliases.AddAliasForTesting(
"remote@loco", "remote@rana", []string{"server"}, aliases.FORWARD)
// Note the pipe aliases are tested below, as they don't use the couriers
// and it can be quite inconvenient to test them in this way.
localC.Expect(2)
remoteC.Expect(1)
_, err := q.Put(tr, "from", []string{"ab@loco", "cd@loco"}, []byte("data"))
remoteC.Expect(3)
// One email from a local domain: from@loco -> ab@loco, cd@loco, fwd@loco.
_, err := q.Put(tr, "from@loco",
[]string{"ab@loco", "cd@loco", "fwd@loco"},
[]byte("data"))
if err != nil {
t.Fatalf("Put: %v", err)
}
// And another from a remote domain: from@rana -> remote@loco
_, err = q.Put(tr, "from@rana",
[]string{"remote@loco"},
[]byte("data"))
if err != nil {
t.Fatalf("Put: %v", err)
}
localC.Wait()
remoteC.Wait()
cases := []struct {
courier *testlib.TestCourier
expectedTo string
courier *testlib.TestCourier
expectedFrom string
expectedTo string
}{
{localC, "pq@loco"},
{localC, "rs@loco"},
{remoteC, "ata@hualpa"},
// From the local domain: from@loco
{localC, "from@loco", "pq@loco"},
{localC, "from@loco", "rs@loco"},
{remoteC, "from@loco", "ata@hualpa"},
{remoteC, "from@loco", "fwd@loco"},
// From the remote domain: from@rana.
// Note the SRS in the remoteC.
{remoteC, "remote+fwd_from=from=rana@loco", "remote@rana"},
}
for _, c := range cases {
req := c.courier.ReqFor[c.expectedTo]
@@ -157,9 +181,9 @@ func TestAliases(t *testing.T) {
continue
}
if req.From != "from" || req.To != c.expectedTo ||
if req.From != c.expectedFrom || req.To != c.expectedTo ||
!bytes.Equal(req.Data, []byte("data")) {
t.Errorf("wrong request for %q: %v", c.expectedTo, req)
t.Errorf("wrong request for %q: %v", c.expectedTo, *req)
}
}
}