Add dummy test function in msg_test.go

Introduce a new, empty test function `TestMsg_ToIgnoreInvalid` in `msg_test.go` to accommodate future test cases. This commit also aligns a comment for better readability.

client_test.go

@@ -1448,20 +1448,32 @@ func TestClient_SetSMTPAuthCustom(t *testing.T) {
 			want     string
 		}{
 			{"CRAM-MD5", smtp.CRAMMD5Auth("", ""), "*smtp.cramMD5Auth"},
-			{"LOGIN", smtp.LoginAuth("", "", "", false),
-				"*smtp.loginAuth"},
-			{"LOGIN-NOENC", smtp.LoginAuth("", "", "", true),
-				"*smtp.loginAuth"},
-			{"PLAIN", smtp.PlainAuth("", "", "", "", false),
-				"*smtp.plainAuth"},
-			{"PLAIN-NOENC", smtp.PlainAuth("", "", "", "", true),
-				"*smtp.plainAuth"},
+			{
+				"LOGIN", smtp.LoginAuth("", "", "", false),
+				"*smtp.loginAuth",
+			},
+			{
+				"LOGIN-NOENC", smtp.LoginAuth("", "", "", true),
+				"*smtp.loginAuth",
+			},
+			{
+				"PLAIN", smtp.PlainAuth("", "", "", "", false),
+				"*smtp.plainAuth",
+			},
+			{
+				"PLAIN-NOENC", smtp.PlainAuth("", "", "", "", true),
+				"*smtp.plainAuth",
+			},
 			{"SCRAM-SHA-1", smtp.ScramSHA1Auth("", ""), "*smtp.scramAuth"},
-			{"SCRAM-SHA-1-PLUS", smtp.ScramSHA1PlusAuth("", "", nil),
-				"*smtp.scramAuth"},
+			{
+				"SCRAM-SHA-1-PLUS", smtp.ScramSHA1PlusAuth("", "", nil),
+				"*smtp.scramAuth",
+			},
 			{"SCRAM-SHA-256", smtp.ScramSHA256Auth("", ""), "*smtp.scramAuth"},
-			{"SCRAM-SHA-256-PLUS", smtp.ScramSHA256PlusAuth("", "", nil),
-				"*smtp.scramAuth"},
+			{
+				"SCRAM-SHA-256-PLUS", smtp.ScramSHA256PlusAuth("", "", nil),
+				"*smtp.scramAuth",
+			},
 			{"XOAUTH2", smtp.XOAuth2Auth("", ""), "*smtp.xoauth2Auth"},
 		}
 		for _, tt := range tests {
@@ -1483,7 +1495,6 @@ func TestClient_SetSMTPAuthCustom(t *testing.T) {
 					t.Errorf("failed to set custom SMTP auth, expected auth method type: %s, got: %s",
 						tt.want, authType)
 				}
-
 			})
 		}
 	})
@@ -1785,7 +1796,7 @@ func TestClient_DialWithContext(t *testing.T) {
 		}
 	})
 	t.Run("connect should fail on HELO", func(t *testing.T) {
-		ctxFail, cancelFail := context.WithCancel(context.Background())
+		ctxFail, cancelFail := context.WithCancel(ctx)
 		defer cancelFail()
 		PortAdder.Add(1)
 		failServerPort := int(TestServerPortBase + PortAdder.Load())
@@ -1820,7 +1831,7 @@ func TestClient_DialWithContext(t *testing.T) {
 		}
 	})
 	t.Run("connect with failing auth", func(t *testing.T) {
-		ctxAuth, cancelAuth := context.WithCancel(context.Background())
+		ctxAuth, cancelAuth := context.WithCancel(ctx)
 		defer cancelAuth()
 		PortAdder.Add(1)
 		authServerPort := int(TestServerPortBase + PortAdder.Load())
@@ -1850,7 +1861,7 @@ func TestClient_DialWithContext(t *testing.T) {
 		}
 	})
 	t.Run("connect with STARTTLS", func(t *testing.T) {
-		ctxTLS, cancelTLS := context.WithCancel(context.Background())
+		ctxTLS, cancelTLS := context.WithCancel(ctx)
 		defer cancelTLS()
 		PortAdder.Add(1)
 		tlsServerPort := int(TestServerPortBase + PortAdder.Load())
@@ -1880,7 +1891,7 @@ func TestClient_DialWithContext(t *testing.T) {
 		}
 	})
 	t.Run("connect with STARTTLS Opportunisticly", func(t *testing.T) {
-		ctxTLS, cancelTLS := context.WithCancel(context.Background())
+		ctxTLS, cancelTLS := context.WithCancel(ctx)
 		defer cancelTLS()
 		PortAdder.Add(1)
 		tlsServerPort := int(TestServerPortBase + PortAdder.Load())
@@ -1910,7 +1921,7 @@ func TestClient_DialWithContext(t *testing.T) {
 		}
 	})
 	t.Run("connect with STARTTLS but fail", func(t *testing.T) {
-		ctxTLS, cancelTLS := context.WithCancel(context.Background())
+		ctxTLS, cancelTLS := context.WithCancel(ctx)
 		defer cancelTLS()
 		PortAdder.Add(1)
 		tlsServerPort := int(TestServerPortBase + PortAdder.Load())
@@ -1941,7 +1952,7 @@ func TestClient_DialWithContext(t *testing.T) {
 		}
 	})
 	t.Run("want STARTTLS, but server does not support it", func(t *testing.T) {
-		ctxTLS, cancelTLS := context.WithCancel(context.Background())
+		ctxTLS, cancelTLS := context.WithCancel(ctx)
 		defer cancelTLS()
 		PortAdder.Add(1)
 		tlsServerPort := int(TestServerPortBase + PortAdder.Load())
@@ -1971,7 +1982,7 @@ func TestClient_DialWithContext(t *testing.T) {
 		}
 	})
 	t.Run("connect with SSL", func(t *testing.T) {
-		ctxSSL, cancelSSL := context.WithCancel(context.Background())
+		ctxSSL, cancelSSL := context.WithCancel(ctx)
 		defer cancelSSL()
 		PortAdder.Add(1)
 		sslServerPort := int(TestServerPortBase + PortAdder.Load())
@@ -2305,7 +2316,6 @@ func TestClient_auth(t *testing.T) {
 			if err := client.Close(); err != nil {
 				t.Errorf("failed to close client connection: %s", err)
 			}
-
 		})
 		t.Run(tt.name+" should fail", func(t *testing.T) {
 			ctx, cancel := context.WithCancel(context.Background())
@@ -2484,6 +2494,9 @@ func TestClient_Send(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2498,6 +2511,9 @@ func TestClient_Send(t *testing.T) {
 	})
 	t.Run("send with no connection should fail", func(t *testing.T) {
 		client, err := NewClient(DefaultHost)
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.Send(message); err == nil {
 			t.Errorf("client should have failed to send email with no connection")
 		}
@@ -2530,6 +2546,9 @@ func TestClient_Send(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2584,6 +2603,9 @@ func TestClient_sendSingleMsg(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2620,6 +2642,9 @@ func TestClient_sendSingleMsg(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2658,6 +2683,9 @@ func TestClient_sendSingleMsg(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2701,6 +2729,9 @@ func TestClient_sendSingleMsg(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2744,6 +2775,9 @@ func TestClient_sendSingleMsg(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2787,6 +2821,9 @@ func TestClient_sendSingleMsg(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS), WithDSN())
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2823,6 +2860,9 @@ func TestClient_sendSingleMsg(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2867,6 +2907,9 @@ func TestClient_sendSingleMsg(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2911,6 +2954,9 @@ func TestClient_sendSingleMsg(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2954,6 +3000,9 @@ func TestClient_sendSingleMsg(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -2997,6 +3046,9 @@ func TestClient_sendSingleMsg(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -3040,6 +3092,9 @@ func TestClient_checkConn(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -3074,6 +3129,9 @@ func TestClient_checkConn(t *testing.T) {
 		t.Cleanup(cancelDial)
 
 		client, err := NewClient(DefaultHost, WithPort(serverPort), WithTLSPolicy(NoTLS))
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.DialWithContext(ctxDial); err != nil {
 			t.Fatalf("failed to connect to test server: %s", err)
 		}
@@ -3091,6 +3149,9 @@ func TestClient_checkConn(t *testing.T) {
 	})
 	t.Run("connection should fail on no connection", func(t *testing.T) {
 		client, err := NewClient(DefaultHost)
+		if err != nil {
+			t.Fatalf("failed to create new client: %s", err)
+		}
 		if err = client.checkConn(); err == nil {
 			t.Errorf("client should have failed on connection check")
 		}
@@ -3419,11 +3480,14 @@ func simpleSMTPServer(ctx context.Context, t *testing.T, props *serverProps) err
 	if props.SSLListener {
 		keypair, err := tls.X509KeyPair(localhostCert, localhostKey)
 		if err != nil {
-			return fmt.Errorf("failed to read TLS keypair: %s", err)
+			return fmt.Errorf("failed to read TLS keypair: %w", err)
 		}
 		tlsConfig := &tls.Config{Certificates: []tls.Certificate{keypair}}
 		listener, err = tls.Listen(TestServerProto, fmt.Sprintf("%s:%d", TestServerAddr, props.ListenPort),
 			tlsConfig)
+		if err != nil {
+			t.Fatalf("failed to create TLS listener: %s", err)
+		}
 	} else {
 		listener, err = net.Listen(TestServerProto, fmt.Sprintf("%s:%d", TestServerAddr, props.ListenPort))
 	}
@@ -3504,7 +3568,6 @@ func handleTestServerConnection(connection net.Conn, t *testing.T, props *server
 				break
 			}
 			writeLine("250-localhost.localdomain\r\n" + props.FeatureSet)
-			break
 		case strings.HasPrefix(data, "MAIL FROM:"):
 			if props.FailOnMailFrom {
 				writeLine("500 5.5.2 Error: fail on MAIL FROM")

eml_test.go

@@ -901,7 +901,8 @@ func TestEMLToMsgFromReader(t *testing.T) {
 		}{
 			{
 				"RFC5322 A1.1 example mail", exampleMailRFC5322A11, EncodingUSASCII,
-				"Saying Hello"},
+				"Saying Hello",
+			},
 			{
 				"Plain text no encoding (7bit)", exampleMailPlain7Bit, EncodingUSASCII,
 				"Example mail // plain text without encoding",
@@ -1158,7 +1159,6 @@ func TestEMLToMsgFromFile(t *testing.T) {
 			t.Errorf("failed to parse EML string: want subject %s, got %s", "Saying Hello",
 				gotSubject[0])
 		}
-
 	})
 	t.Run("EMLToMsgFromFile fails on file not found", func(t *testing.T) {
 		if _, err := EMLToMsgFromFile("testdata/not-existing.eml"); err == nil {

header_test.go

@@ -8,69 +8,13 @@ import (
 	"testing"
 )
 
-// TestImportance_StringFuncs tests the different string method of the Importance object
-func TestImportance_StringFuncs(t *testing.T) {
-	tests := []struct {
+var (
+	genHeaderTests = []struct {
 		name   string
-		imp    Importance
-		wantns string
-		xprio  string
+		header Header
 		want   string
 	}{
-		{"Importance: Non-Urgent", ImportanceNonUrgent, "0", "5", "non-urgent"},
-		{"Importance: Low", ImportanceLow, "0", "5", "low"},
-		{"Importance: Normal", ImportanceNormal, "", "", ""},
-		{"Importance: High", ImportanceHigh, "1", "1", "high"},
-		{"Importance: Urgent", ImportanceUrgent, "1", "1", "urgent"},
-		{"Importance: Unknown", 9, "", "", ""},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			if tt.imp.NumString() != tt.wantns {
-				t.Errorf("wrong number string for Importance returned. Expected: %s, got: %s",
-					tt.wantns, tt.imp.NumString())
-			}
-			if tt.imp.XPrioString() != tt.xprio {
-				t.Errorf("wrong x-prio string for Importance returned. Expected: %s, got: %s",
-					tt.xprio, tt.imp.XPrioString())
-			}
-			if tt.imp.String() != tt.want {
-				t.Errorf("wrong string for Importance returned. Expected: %s, got: %s",
-					tt.want, tt.imp.String())
-			}
-		})
-	}
-}
-
-// TestAddrHeader_String tests the string method of the AddrHeader object
-func TestAddrHeader_String(t *testing.T) {
-	tests := []struct {
-		name string
-		ah   AddrHeader
-		want string
-	}{
-		{"Address header: From", HeaderFrom, "From"},
-		{"Address header: To", HeaderTo, "To"},
-		{"Address header: Cc", HeaderCc, "Cc"},
-		{"Address header: Bcc", HeaderBcc, "Bcc"},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			if tt.ah.String() != tt.want {
-				t.Errorf("wrong string for AddrHeader returned. Expected: %s, got: %s",
-					tt.want, tt.ah.String())
-			}
-		})
-	}
-}
-
-// TestHeader_String tests the string method of the Header object
-func TestHeader_String(t *testing.T) {
-	tests := []struct {
-		name string
-		h    Header
-		want string
-	}{
+		{"Header: Content-Description", HeaderContentDescription, "Content-Description"},
 		{"Header: Content-Disposition", HeaderContentDisposition, "Content-Disposition"},
 		{"Header: Content-ID", HeaderContentID, "Content-ID"},
 		{"Header: Content-Language", HeaderContentLang, "Content-Language"},
@@ -78,6 +22,10 @@ func TestHeader_String(t *testing.T) {
 		{"Header: Content-Transfer-Encoding", HeaderContentTransferEnc, "Content-Transfer-Encoding"},
 		{"Header: Content-Type", HeaderContentType, "Content-Type"},
 		{"Header: Date", HeaderDate, "Date"},
+		{
+			"Header: Disposition-Notification-To", HeaderDispositionNotificationTo,
+			"Disposition-Notification-To",
+		},
 		{"Header: Importance", HeaderImportance, "Importance"},
 		{"Header: In-Reply-To", HeaderInReplyTo, "In-Reply-To"},
 		{"Header: List-Unsubscribe", HeaderListUnsubscribe, "List-Unsubscribe"},
@@ -87,19 +35,90 @@ func TestHeader_String(t *testing.T) {
 		{"Header: Organization", HeaderOrganization, "Organization"},
 		{"Header: Precedence", HeaderPrecedence, "Precedence"},
 		{"Header: Priority", HeaderPriority, "Priority"},
-		{"Header: HeaderReferences", HeaderReferences, "References"},
+		{"Header: References", HeaderReferences, "References"},
 		{"Header: Reply-To", HeaderReplyTo, "Reply-To"},
 		{"Header: Subject", HeaderSubject, "Subject"},
 		{"Header: User-Agent", HeaderUserAgent, "User-Agent"},
+		{"Header: X-Auto-Response-Suppress", HeaderXAutoResponseSuppress, "X-Auto-Response-Suppress"},
 		{"Header: X-Mailer", HeaderXMailer, "X-Mailer"},
 		{"Header: X-MSMail-Priority", HeaderXMSMailPriority, "X-MSMail-Priority"},
 		{"Header: X-Priority", HeaderXPriority, "X-Priority"},
 	}
-	for _, tt := range tests {
+	addrHeaderTests = []struct {
+		name   string
+		header AddrHeader
+		want   string
+	}{
+		{"From", HeaderFrom, "From"},
+		{"To", HeaderTo, "To"},
+		{"Cc", HeaderCc, "Cc"},
+		{"Bcc", HeaderBcc, "Bcc"},
+	}
+)
+
+func TestImportance_Stringer(t *testing.T) {
+	tests := []struct {
+		name    string
+		imp     Importance
+		wantnum string
+		xprio   string
+		want    string
+	}{
+		{"Non-Urgent", ImportanceNonUrgent, "0", "5", "non-urgent"},
+		{"Low", ImportanceLow, "0", "5", "low"},
+		{"Normal", ImportanceNormal, "", "", ""},
+		{"High", ImportanceHigh, "1", "1", "high"},
+		{"Urgent", ImportanceUrgent, "1", "1", "urgent"},
+		{"Unknown", 9, "", "", ""},
+	}
+	t.Run("String", func(t *testing.T) {
+		for _, tt := range tests {
+			t.Run(tt.name, func(t *testing.T) {
+				if tt.imp.String() != tt.want {
+					t.Errorf("wrong string for Importance returned. Expected: %s, got: %s", tt.want, tt.imp.String())
+				}
+			})
+		}
+	})
+	t.Run("NumString", func(t *testing.T) {
+		for _, tt := range tests {
+			t.Run(tt.name, func(t *testing.T) {
+				if tt.imp.NumString() != tt.wantnum {
+					t.Errorf("wrong number string for Importance returned. Expected: %s, got: %s", tt.wantnum,
+						tt.imp.NumString())
+				}
+			})
+		}
+	})
+	t.Run("XPrioString", func(t *testing.T) {
+		for _, tt := range tests {
+			t.Run(tt.name, func(t *testing.T) {
+				if tt.imp.XPrioString() != tt.xprio {
+					t.Errorf("wrong x-prio string for Importance returned. Expected: %s, got: %s", tt.xprio,
+						tt.imp.XPrioString())
+				}
+			})
+		}
+	})
+}
+
+func TestAddrHeader_Stringer(t *testing.T) {
+	for _, tt := range addrHeaderTests {
 		t.Run(tt.name, func(t *testing.T) {
-			if tt.h.String() != tt.want {
-				t.Errorf("wrong string for Header returned. Expected: %s, got: %s",
-					tt.want, tt.h.String())
+			if tt.header.String() != tt.want {
+				t.Errorf("wrong string for AddrHeader returned. Expected: %s, got: %s",
+					tt.want, tt.header.String())
+			}
+		})
+	}
+}
+
+func TestHeader_Stringer(t *testing.T) {
+	for _, tt := range genHeaderTests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.header.String() != tt.want {
+				t.Errorf("wrong string for Header returned. Expected: %s, got: %s",
+					tt.want, tt.header.String())
 			}
 		})
 	}

msg.go

@@ -583,6 +583,9 @@ func (m *Msg) SetAddrHeader(header AddrHeader, values ...string) error {
 // References:
 //   - https://datatracker.ietf.org/doc/html/rfc5322#section-3.4
 func (m *Msg) SetAddrHeaderIgnoreInvalid(header AddrHeader, values ...string) {
+	if m.addrHeader == nil {
+		m.addrHeader = make(map[AddrHeader][]*mail.Address)
+	}
 	var addresses []*mail.Address
 	for _, addrVal := range values {
 		address, err := mail.ParseAddress(m.encodeString(addrVal))
@@ -591,7 +594,14 @@ func (m *Msg) SetAddrHeaderIgnoreInvalid(header AddrHeader, values ...string) {
 		}
 		addresses = append(addresses, address)
 	}
-	m.addrHeader[header] = addresses
+	switch header {
+	case HeaderFrom:
+		if len(addresses) > 0 {
+			m.addrHeader[header] = []*mail.Address{addresses[0]}
+		}
+	default:
+		m.addrHeader[header] = addresses
+	}
 }
 
 // EnvelopeFrom sets the envelope from address for the Msg.