修复本域有效签名邮件因SPF失败被误删

backend/dto/parsemail/dkim.go

@@ -120,23 +120,33 @@ func (p *Dkim) Sign(msgData string) ([]byte, error) {
 }
 
 func Check(ctx *context.Context, mail io.Reader) bool {
+	return CheckForDomain(ctx, mail, "")
+}
 
-	verifications, err := dkim.Verify(mail)
+// CheckForDomain 在指定域名时要求有效签名与发件域严格一致，避免其他域签名冒用本域。
+func CheckForDomain(ctx *context.Context, mail io.Reader, domain string) bool {
+	return checkForDomain(ctx, mail, domain, nil)
+}
+
+func checkForDomain(ctx *context.Context, mail io.Reader, domain string, options *dkim.VerifyOptions) bool {
+	verifications, err := dkim.VerifyWithOptions(mail, options)
 	if err != nil {
 		log.WithContext(ctx).Warnf("DKIM Error:%v", err)
-	}
-
-	if len(verifications) == 0 {
 		return false
 	}
-
+	domain = strings.TrimSpace(domain)
 	for _, v := range verifications {
+		if v == nil {
+			continue
+		}
 		if v.Err == nil {
 			log.Println("Valid signature for:", v.Domain)
+			if domain == "" || strings.EqualFold(v.Domain, domain) {
+				return true
+			}
 		} else {
 			log.Println("Invalid signature for:", v.Domain, v.Err)
-			return false
 		}
 	}
-	return true
+	return false
 }

backend/dto/parsemail/dkim_security_test.go

@@ -1,19 +1,70 @@
 package parsemail
 
 import (
+	"bytes"
 	"crypto/ecdsa"
 	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/rsa"
 	"crypto/x509"
+	"encoding/base64"
 	"encoding/pem"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"git.pcux.cn/xuans/Smail/config"
+	"github.com/emersion/go-msgauth/dkim"
 )
 
+func TestCheckForDomainRequiresValidAlignedSignature(t *testing.T) {
+	key, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatal(err)
+	}
+	publicKey, err := x509.MarshalPKIXPublicKey(&key.PublicKey)
+	if err != nil {
+		t.Fatal(err)
+	}
+	options := &dkim.VerifyOptions{LookupTXT: func(domain string) ([]string, error) {
+		return []string{"v=DKIM1; k=rsa; p=" + base64.StdEncoding.EncodeToString(publicKey)}, nil
+	}}
+	message := "From: sender@example.com\r\nTo: recipient@example.com\r\nSubject: authentication\r\n\r\noriginal body\r\n"
+	for _, tc := range []struct {
+		name, signer, expected string
+		tampered               bool
+		want                   bool
+	}{
+		{name: "aligned", signer: "example.com", expected: "example.com", want: true},
+		{name: "case_insensitive", signer: "example.com", expected: "EXAMPLE.COM", want: true},
+		{name: "foreign_domain", signer: "other.example", expected: "example.com"},
+		{name: "subdomain", signer: "sub.example.com", expected: "example.com"},
+		{name: "suffix_attack", signer: "example.com.other.example", expected: "example.com"},
+		{name: "invalid_signature", signer: "example.com", expected: "example.com", tampered: true},
+		{name: "generic_verification", signer: "other.example", want: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			var signed bytes.Buffer
+			if err := dkim.Sign(&signed, strings.NewReader(message), &dkim.SignOptions{
+				Domain: tc.signer, Selector: "default", Signer: key,
+			}); err != nil {
+				t.Fatal(err)
+			}
+			data := signed.String()
+			if tc.tampered {
+				data += "tampered body\r\n"
+			}
+			if got := checkForDomain(nil, strings.NewReader(data), tc.expected, options); got != tc.want {
+				t.Fatalf("签名认证结果为 %v，期望 %v", got, tc.want)
+			}
+		})
+	}
+	if checkForDomain(nil, strings.NewReader(message), "example.com", options) {
+		t.Fatal("未签名邮件不能通过认证")
+	}
+}
+
 func TestLoadPrivateKeyAcceptsStrongRSAKey(t *testing.T) {
 	path := writeDKIMTestKey(t, 2048)
 	signer, err := loadPrivateKey(path)

backend/listen/smtp_server/read_content.go

@@ -192,17 +192,20 @@ func (s *Session) Data(r io.Reader) (resultErr error) {
 		var dkimStatus, SPFStatus bool
 
 		details.Stage = "验证收信身份与插件处理"
+		_, fromDomain := email.From.GetDomainAccount()
+		domains := config.CurrentMailDomains()
+		localSender := array.InArray(fromDomain, domains.Accepted)
+		dkimDomain := ""
+		if localSender {
+			dkimDomain = fromDomain
+		}
 		// DKIM校验
-		dkimStatus = parsemail.Check(ctx, bytes.NewReader(emailData))
+		dkimStatus = parsemail.CheckForDomain(ctx, bytes.NewReader(emailData), dkimDomain)
 
 		SPFStatus = spfCheck(s.RemoteAddress.String(), email.Sender, email.Sender.EmailAddress)
 
-		_, formDomain := email.From.GetDomainAccount()
-		domains := config.CurrentMailDomains()
-		spoofed := array.InArray(formDomain, domains.Accepted) && SPFStatus == false
-		if spoofed {
-			dkimStatus = false
-		}
+		// 本机投递也保留真实 SPF 结果，仅有效且同域的 DKIM 签名可以避免误判伪造。
+		spoofed := localSender && !SPFStatus && !dkimStatus
 		email.Authentication = parsemail.NewEmailAuthentication(SPFStatus, dkimStatus)
 
 		log.WithContext(ctx).Debugf("开始执行插件ReceiveParseAfter！")