Make receiver hostname configurable via --receiver-hostname flag

Remove the package-level global hostname from parser.go.

Adds a log warning when the last Received hop doesn't match the
expected receiver hostname.

Bug: https://github.com/happyDomain/happydeliver/issues/11

internal/config/cli.go

@@ -34,6 +34,7 @@ func declareFlags(o *Config) {
 	flag.StringVar(&o.Email.Domain, "domain", o.Email.Domain, "Domain used to receive emails")
 	flag.StringVar(&o.Email.TestAddressPrefix, "address-prefix", o.Email.TestAddressPrefix, "Expected email adress prefix (deny address that doesn't start with this prefix)")
 	flag.StringVar(&o.Email.LMTPAddr, "lmtp-addr", o.Email.LMTPAddr, "LMTP server listen address")
+	flag.StringVar(&o.Email.ReceiverHostname, "receiver-hostname", o.Email.ReceiverHostname, "Hostname used to filter Authentication-Results headers (defaults to os.Hostname())")
 	flag.DurationVar(&o.Analysis.DNSTimeout, "dns-timeout", o.Analysis.DNSTimeout, "Timeout when performing DNS query")
 	flag.DurationVar(&o.Analysis.HTTPTimeout, "http-timeout", o.Analysis.HTTPTimeout, "Timeout when performing HTTP query")
 	flag.Var(&StringArray{&o.Analysis.RBLs}, "rbl", "Append a RBL (use this option multiple time to append multiple RBLs)")

internal/config/config.go

@@ -34,6 +34,11 @@ import (
 	openapi_types "github.com/oapi-codegen/runtime/types"
 )
 
+func getHostname() string {
+	h, _ := os.Hostname()
+	return h
+}
+
 // Config represents the application configuration
 type Config struct {
 	DevProxy        string
@@ -58,6 +63,7 @@ type EmailConfig struct {
 	Domain            string
 	TestAddressPrefix string
 	LMTPAddr          string
+	ReceiverHostname  string
 }
 
 // AnalysisConfig contains timeout and behavior settings for email analysis
@@ -84,6 +90,7 @@ func DefaultConfig() *Config {
 			Domain:            "happydeliver.local",
 			TestAddressPrefix: "test-",
 			LMTPAddr:          "127.0.0.1:2525",
+			ReceiverHostname:  getHostname(),
 		},
 		Analysis: AnalysisConfig{
 			DNSTimeout:  5 * time.Second,

internal/receiver/receiver.go

@@ -98,6 +98,17 @@ func (r *EmailReceiver) ProcessEmailBytes(rawEmail []byte, recipientEmail string
 
 	log.Printf("Analysis complete. Grade: %s. Score: %d/100", result.Report.Grade, result.Report.Score)
 
+	// Warn if the last Received hop doesn't match the expected receiver hostname
+	if r.config.Email.ReceiverHostname != "" &&
+		result.Report.HeaderAnalysis != nil &&
+		result.Report.HeaderAnalysis.ReceivedChain != nil &&
+		len(*result.Report.HeaderAnalysis.ReceivedChain) > 0 {
+		lastHop := (*result.Report.HeaderAnalysis.ReceivedChain)[0]
+		if lastHop.By != nil && *lastHop.By != r.config.Email.ReceiverHostname {
+			log.Printf("WARNING: Last Received hop 'by' field (%s) does not match expected receiver hostname (%s): check your RECEIVER_HOSTNAME config as authentication results will be false", *lastHop.By, r.config.Email.ReceiverHostname)
+		}
+	}
+
 	// Marshal report to JSON
 	reportJSON, err := json.Marshal(result.Report)
 	if err != nil {

pkg/analyzer/analyzer.go

@@ -41,6 +41,7 @@ type EmailAnalyzer struct {
 // NewEmailAnalyzer creates a new email analyzer with the given configuration
 func NewEmailAnalyzer(cfg *config.Config) *EmailAnalyzer {
 	generator := NewReportGenerator(
+		cfg.Email.ReceiverHostname,
 		cfg.Analysis.DNSTimeout,
 		cfg.Analysis.HTTPTimeout,
 		cfg.Analysis.RBLs,

pkg/analyzer/authentication.go

@@ -28,11 +28,13 @@ import (
 )
 
 // AuthenticationAnalyzer analyzes email authentication results
-type AuthenticationAnalyzer struct{}
+type AuthenticationAnalyzer struct {
+	receiverHostname string
+}
 
 // NewAuthenticationAnalyzer creates a new authentication analyzer
-func NewAuthenticationAnalyzer() *AuthenticationAnalyzer {
+func NewAuthenticationAnalyzer(receiverHostname string) *AuthenticationAnalyzer {
-	return &AuthenticationAnalyzer{}
+	return &AuthenticationAnalyzer{receiverHostname: receiverHostname}
 }
 
 // AnalyzeAuthentication extracts and analyzes authentication results from email headers
@@ -40,7 +42,7 @@ func (a *AuthenticationAnalyzer) AnalyzeAuthentication(email *EmailMessage) *api
 	results := &api.AuthenticationResults{}
 
 	// Parse Authentication-Results headers
-	authHeaders := email.GetAuthenticationResults()
+	authHeaders := email.GetAuthenticationResults(a.receiverHostname)
 	for _, header := range authHeaders {
 		a.parseAuthenticationResultsHeader(header, results)
 	}

pkg/analyzer/authentication_arc_test.go

@@ -50,7 +50,7 @@ func TestParseARCResult(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -136,7 +136,7 @@ func TestValidateARCChain(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

pkg/analyzer/authentication_bimi_test.go

@@ -64,7 +64,7 @@ func TestParseBIMIResult(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

pkg/analyzer/authentication_dkim_test.go

@@ -58,7 +58,7 @@ func TestParseDKIMResult(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

pkg/analyzer/authentication_dmarc_test.go

@@ -48,7 +48,7 @@ func TestParseDMARCResult(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

pkg/analyzer/authentication_iprev_test.go

@@ -93,7 +93,7 @@ func TestParseIPRevResult(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -181,7 +181,7 @@ func TestParseAuthenticationResultsHeader_IPRev(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

pkg/analyzer/authentication_spf_test.go

@@ -60,7 +60,7 @@ func TestParseSPFResult(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -161,7 +161,7 @@ func TestParseLegacySPF(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

pkg/analyzer/authentication_test.go

@@ -100,7 +100,7 @@ func TestGetAuthenticationScore(t *testing.T) {
 		},
 	}
 
-	scorer := NewAuthenticationAnalyzer()
+	scorer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -247,7 +247,7 @@ func TestParseAuthenticationResultsHeader(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -353,7 +353,7 @@ func TestParseAuthenticationResultsHeader(t *testing.T) {
 
 func TestParseAuthenticationResultsHeader_OnlyFirstResultParsed(t *testing.T) {
 	// This test verifies that only the first occurrence of each auth method is parsed
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	t.Run("Multiple SPF results - only first is parsed", func(t *testing.T) {
 		header := "mail.example.com; spf=pass smtp.mailfrom=first@example.com; spf=fail smtp.mailfrom=second@example.com"

pkg/analyzer/authentication_x_aligned_from_test.go

@@ -66,7 +66,7 @@ func TestParseXAlignedFromResult(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -126,7 +126,7 @@ func TestCalculateXAlignedFromScore(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

pkg/analyzer/authentication_x_google_dkim_test.go

@@ -60,7 +60,7 @@ func TestParseXGoogleDKIMResult(t *testing.T) {
 		},
 	}
 
-	analyzer := NewAuthenticationAnalyzer()
+	analyzer := NewAuthenticationAnalyzer("")
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

pkg/analyzer/parser.go

@@ -28,16 +28,9 @@ import (
 	"mime/multipart"
 	"net/mail"
 	"net/textproto"
-	"os"
 	"strings"
 )
 
-var hostname = ""
-
-func init() {
-	hostname, _ = os.Hostname()
-}
-
 // EmailMessage represents a parsed email message
 type EmailMessage struct {
 	Header     mail.Header
@@ -218,18 +211,18 @@ func buildRawHeaders(header mail.Header) string {
 }
 
 // GetAuthenticationResults extracts Authentication-Results headers
-// If hostname is provided, only returns headers that begin with that hostname
+// If receiverHostname is provided, only returns headers that begin with that hostname
-func (e *EmailMessage) GetAuthenticationResults() []string {
+func (e *EmailMessage) GetAuthenticationResults(receiverHostname string) []string {
 	allResults := e.Header[textproto.CanonicalMIMEHeaderKey("Authentication-Results")]
 
 	// If no hostname specified, return all results
-	if hostname == "" {
+	if receiverHostname == "" {
 		return allResults
 	}
 
 	// Filter results that begin with the specified hostname
 	var filtered []string
-	prefix := hostname + ";"
+	prefix := receiverHostname + ";"
 	for _, result := range allResults {
 		// Trim whitespace and check if it starts with hostname;
 		trimmed := strings.TrimSpace(result)

pkg/analyzer/parser_test.go

@@ -106,9 +106,6 @@ Content-Type: text/html; charset=utf-8
 }
 
 func TestGetAuthenticationResults(t *testing.T) {
-	// Force hostname
-	hostname = "example.com"
-
 	rawEmail := `From: sender@example.com
 To: recipient@example.com
 Subject: Test Email
@@ -123,7 +120,7 @@ Body content.
 		t.Fatalf("Failed to parse email: %v", err)
 	}
 
-	authResults := email.GetAuthenticationResults()
+	authResults := email.GetAuthenticationResults("example.com")
 	if len(authResults) != 2 {
 		t.Errorf("Expected 2 Authentication-Results headers, got: %d", len(authResults))
 	}

pkg/analyzer/report.go

@@ -43,6 +43,7 @@ type ReportGenerator struct {
 
 // NewReportGenerator creates a new report generator
 func NewReportGenerator(
+	receiverHostname string,
 	dnsTimeout time.Duration,
 	httpTimeout time.Duration,
 	rbls []string,
@@ -50,7 +51,7 @@ func NewReportGenerator(
 	checkAllIPs bool,
 ) *ReportGenerator {
 	return &ReportGenerator{
-		authAnalyzer:    NewAuthenticationAnalyzer(),
+		authAnalyzer:    NewAuthenticationAnalyzer(receiverHostname),
 		spamAnalyzer:    NewSpamAssassinAnalyzer(),
 		rspamdAnalyzer:  NewRspamdAnalyzer(),
 		dnsAnalyzer:     NewDNSAnalyzer(dnsTimeout),

pkg/analyzer/report_test.go

@@ -32,7 +32,7 @@ import (
 )
 
 func TestNewReportGenerator(t *testing.T) {
-	gen := NewReportGenerator(10*time.Second, 10*time.Second, DefaultRBLs, DefaultDNSWLs, false)
+	gen := NewReportGenerator("", 10*time.Second, 10*time.Second, DefaultRBLs, DefaultDNSWLs, false)
 	if gen == nil {
 		t.Fatal("Expected report generator, got nil")
 	}
@@ -55,7 +55,7 @@ func TestNewReportGenerator(t *testing.T) {
 }
 
 func TestAnalyzeEmail(t *testing.T) {
-	gen := NewReportGenerator(10*time.Second, 10*time.Second, DefaultRBLs, DefaultDNSWLs, false)
+	gen := NewReportGenerator("", 10*time.Second, 10*time.Second, DefaultRBLs, DefaultDNSWLs, false)
 
 	email := createTestEmail()
 
@@ -75,7 +75,7 @@ func TestAnalyzeEmail(t *testing.T) {
 }
 
 func TestGenerateReport(t *testing.T) {
-	gen := NewReportGenerator(10*time.Second, 10*time.Second, DefaultRBLs, DefaultDNSWLs, false)
+	gen := NewReportGenerator("", 10*time.Second, 10*time.Second, DefaultRBLs, DefaultDNSWLs, false)
 	testID := uuid.New()
 
 	email := createTestEmail()
@@ -130,7 +130,7 @@ func TestGenerateReport(t *testing.T) {
 }
 
 func TestGenerateReportWithSpamAssassin(t *testing.T) {
-	gen := NewReportGenerator(10*time.Second, 10*time.Second, DefaultRBLs, DefaultDNSWLs, false)
+	gen := NewReportGenerator("", 10*time.Second, 10*time.Second, DefaultRBLs, DefaultDNSWLs, false)
 	testID := uuid.New()
 
 	email := createTestEmailWithSpamAssassin()
@@ -150,7 +150,7 @@ func TestGenerateReportWithSpamAssassin(t *testing.T) {
 }
 
 func TestGenerateRawEmail(t *testing.T) {
-	gen := NewReportGenerator(10*time.Second, 10*time.Second, DefaultRBLs, DefaultDNSWLs, false)
+	gen := NewReportGenerator("", 10*time.Second, 10*time.Second, DefaultRBLs, DefaultDNSWLs, false)
 
 	tests := []struct {
 		name     string