diff --git a/sime.go b/smime.go
similarity index 81%
rename from sime.go
rename to smime.go
index de2decc..e92d283 100644
--- a/sime.go
+++ b/smime.go
@@ -16,9 +16,6 @@ var (
 	// ErrInvalidKeyPair should be used if key pair is invalid
 	ErrInvalidKeyPair = errors.New("invalid key pair")
 
-	// ErrInvalidCertificate should be used if a certificate is invalid
-	ErrInvalidCertificate = errors.New("invalid certificate")
-
 	// ErrCouldNotInitialize should be used if the signed data could not initialize
 	ErrCouldNotInitialize = errors.New("could not initialize signed data")
 
@@ -34,9 +31,8 @@ var (
 
 // SMime is used to sign messages with S/MIME
 type SMime struct {
-	privateKey         *rsa.PrivateKey
-	certificate        *x509.Certificate
-	parentCertificates []*x509.Certificate
+	privateKey  *rsa.PrivateKey
+	certificate *x509.Certificate
 }
 
 // NewSMime construct a new instance of SMime with a provided *tls.Certificate
@@ -45,19 +41,9 @@ func newSMime(keyPair *tls.Certificate) (*SMime, error) {
 		return nil, ErrInvalidKeyPair
 	}
 
-	parentCertificates := make([]*x509.Certificate, 0)
-	for _, cert := range keyPair.Certificate[1:] {
-		c, err := x509.ParseCertificate(cert)
-		if err != nil {
-			return nil, ErrInvalidCertificate
-		}
-		parentCertificates = append(parentCertificates, c)
-	}
-
 	return &SMime{
-		privateKey:         keyPair.PrivateKey.(*rsa.PrivateKey),
-		certificate:        keyPair.Leaf,
-		parentCertificates: parentCertificates,
+		privateKey:  keyPair.PrivateKey.(*rsa.PrivateKey),
+		certificate: keyPair.Leaf,
 	}, nil
 }
 
@@ -72,7 +58,7 @@ func (sm *SMime) signMessage(message string) (*string, error) {
 		return nil, ErrCouldNotInitialize
 	}
 
-	if err = signedData.AddSignerChain(sm.certificate, sm.privateKey, sm.parentCertificates, pkcs7.SignerInfoConfig{}); err != nil {
+	if err = signedData.AddSigner(sm.certificate, sm.privateKey, pkcs7.SignerInfoConfig{}); err != nil {
 		return nil, ErrCouldNotAddSigner
 	}
 
@@ -92,7 +78,7 @@ func (sm *SMime) signMessage(message string) (*string, error) {
 }
 
 // createMessage prepares the message that will be used for the sign method later
-func (sm *SMime) createMessage(encoding Encoding, contentType ContentType, charset Charset, body []byte) string {
+func (sm *SMime) prepareMessage(encoding Encoding, contentType ContentType, charset Charset, body []byte) string {
 	return fmt.Sprintf("Content-Transfer-Encoding: %v\r\nContent-Type: %v; charset=%v\r\n\r\n%v", encoding, contentType, charset, string(body))
 }
 
diff --git a/smime_test.go b/smime_test.go
index bd0282d..cfd8518 100644
--- a/smime_test.go
+++ b/smime_test.go
@@ -1,7 +1,8 @@
 package mail
 
 import (
-	"errors"
+	"bytes"
+	"encoding/base64"
 	"fmt"
 	"strings"
 	"testing"
@@ -25,9 +26,6 @@ func TestNewSMime(t *testing.T) {
 	if sMime.certificate != keyPair.Leaf {
 		t.Errorf("NewSMime() did not return the same leaf certificate")
 	}
-	if len(sMime.parentCertificates) != len(keyPair.Certificate)-1 {
-		t.Errorf("NewSMime() did not return the same number of parentCertificates")
-	}
 }
 
 // TestSign tests the sign method
@@ -41,11 +39,20 @@ func TestSign(t *testing.T) {
 	if err != nil {
 		t.Errorf("Error creating new SMime from keyPair: %s", err)
 	}
-	fmt.Println(sMime)
+
+	message := "This is a test message"
+	singedMessage, err := sMime.signMessage(message)
+	if err != nil {
+		t.Errorf("Error creating singed message: %s", err)
+	}
+
+	if *singedMessage == message {
+		t.Errorf("Sign() did not work")
+	}
 }
 
-// TestCreateMessage tests the createMessage method
-func TestCreateMessage(t *testing.T) {
+// TestPrepareMessage tests the createMessage method
+func TestPrepareMessage(t *testing.T) {
 	keyPair, err := getDummyCertificate()
 	if err != nil {
 		t.Errorf("Error getting dummy certificate: %s", err)
@@ -60,7 +67,7 @@ func TestCreateMessage(t *testing.T) {
 	contentType := TypeTextPlain
 	charset := CharsetUTF8
 	body := []byte("This is the body!")
-	result := sMime.createMessage(encoding, contentType, body)
+	result := sMime.prepareMessage(encoding, contentType, charset, body)
 
 	if !strings.Contains(result, encoding.String()) {
 		t.Errorf("createMessage() did not return the correct encoding")
@@ -71,86 +78,113 @@ func TestCreateMessage(t *testing.T) {
 	if !strings.Contains(result, string(body)) {
 		t.Errorf("createMessage() did not return the correct body")
 	}
-	if result != fmt.Sprintf("Content-Transfer-Encoding: %v\r\nContent-Type: %v; charset=%v\r\n\r\n%v", encoding, contentType, charset, string(body)) {
+	if result != fmt.Sprintf("Content-Transfer-Encoding: %s\r\nContent-Type: %s; charset=%s\r\n\r\n%s", encoding, contentType, charset, string(body)) {
 		t.Errorf("createMessage() did not sucessfully create the message")
 	}
 }
 
 // TestEncodeToPEM tests the encodeToPEM method
 func TestEncodeToPEM(t *testing.T) {
+	message := []byte("This is a test message")
 
-	keyPair, err := getDummyCertificate()
+	pemMessage, err := encodeToPEM(message)
 	if err != nil {
-		t.Errorf("Error getting dummy certificate: %s", err)
+		t.Errorf("Error encoding message: %s", err)
 	}
 
-	sMime, err := newSMime(keyPair)
-	if err != nil {
-		t.Errorf("Error creating new SMime from keyPair: %s", err)
+	base64Encoded := base64.StdEncoding.EncodeToString(message)
+	if *pemMessage != base64Encoded {
+		t.Errorf("encodeToPEM() did not work")
 	}
-	fmt.Println(sMime)
 }
 
 // TestBytesFromLines tests the bytesFromLines method
 func TestBytesFromLines(t *testing.T) {
+	ls := lines{
+		{line: []byte("Hello"), endOfLine: []byte("\n")},
+		{line: []byte("World"), endOfLine: []byte("\n")},
+	}
+	expected := []byte("Hello\nWorld\n")
 
+	result := ls.bytesFromLines([]byte("\n"))
+	if !bytes.Equal(result, expected) {
+		t.Errorf("Expected %s, but got %s", expected, result)
+	}
+}
+
+// FuzzBytesFromLines tests the bytesFromLines method with fuzzing
+func FuzzBytesFromLines(f *testing.F) {
+	f.Add([]byte("Hello"), []byte("\n"))
+	f.Fuzz(func(t *testing.T, lineData, sep []byte) {
+		ls := lines{
+			{line: lineData, endOfLine: sep},
+		}
+		_ = ls.bytesFromLines(sep)
+	})
 }
 
 // TestParseLines tests the parseLines method
 func TestParseLines(t *testing.T) {
+	input := []byte("Hello\r\nWorld\nHello\rWorld")
+	expected := lines{
+		{line: []byte("Hello"), endOfLine: []byte("\r\n")},
+		{line: []byte("World"), endOfLine: []byte("\n")},
+		{line: []byte("Hello"), endOfLine: []byte("\r")},
+		{line: []byte("World"), endOfLine: []byte("")},
+	}
 
+	result := parseLines(input)
+	if len(result) != len(expected) {
+		t.Errorf("Expected %d lines, but got %d", len(expected), len(result))
+	}
+
+	for i := range result {
+		if !bytes.Equal(result[i].line, expected[i].line) || !bytes.Equal(result[i].endOfLine, expected[i].endOfLine) {
+			t.Errorf("Line %d mismatch. Expected line: %s, endOfLine: %s, got line: %s, endOfLine: %s",
+				i, expected[i].line, expected[i].endOfLine, result[i].line, result[i].endOfLine)
+		}
+	}
+}
+
+// FuzzParseLines tests the parseLines method with fuzzing
+func FuzzParseLines(f *testing.F) {
+	f.Add([]byte("Hello\nWorld\r\nAnother\rLine"))
+	f.Fuzz(func(t *testing.T, input []byte) {
+		_ = parseLines(input)
+	})
 }
 
 // TestSplitLine tests the splitLine method
 func TestSplitLine(t *testing.T) {
-
-}
-
-func foo(t *testing.T) {
-	tl := []struct {
-		n  string
-		r  SendErrReason
-		te bool
-	}{
-		{"ErrGetSender/temp", ErrGetSender, true},
-		{"ErrGetSender/perm", ErrGetSender, false},
-		{"ErrGetRcpts/temp", ErrGetRcpts, true},
-		{"ErrGetRcpts/perm", ErrGetRcpts, false},
-		{"ErrSMTPMailFrom/temp", ErrSMTPMailFrom, true},
-		{"ErrSMTPMailFrom/perm", ErrSMTPMailFrom, false},
-		{"ErrSMTPRcptTo/temp", ErrSMTPRcptTo, true},
-		{"ErrSMTPRcptTo/perm", ErrSMTPRcptTo, false},
-		{"ErrSMTPData/temp", ErrSMTPData, true},
-		{"ErrSMTPData/perm", ErrSMTPData, false},
-		{"ErrSMTPDataClose/temp", ErrSMTPDataClose, true},
-		{"ErrSMTPDataClose/perm", ErrSMTPDataClose, false},
-		{"ErrSMTPReset/temp", ErrSMTPReset, true},
-		{"ErrSMTPReset/perm", ErrSMTPReset, false},
-		{"ErrWriteContent/temp", ErrWriteContent, true},
-		{"ErrWriteContent/perm", ErrWriteContent, false},
-		{"ErrConnCheck/temp", ErrConnCheck, true},
-		{"ErrConnCheck/perm", ErrConnCheck, false},
-		{"ErrNoUnencoded/temp", ErrNoUnencoded, true},
-		{"ErrNoUnencoded/perm", ErrNoUnencoded, false},
-		{"ErrAmbiguous/temp", ErrAmbiguous, true},
-		{"ErrAmbiguous/perm", ErrAmbiguous, false},
-		{"Unknown/temp", 9999, true},
-		{"Unknown/perm", 9999, false},
+	ls := lines{
+		{line: []byte("Hello\r\nWorld\r\nAnotherLine"), endOfLine: []byte("")},
+	}
+	expected := lines{
+		{line: []byte("Hello"), endOfLine: []byte("\r\n")},
+		{line: []byte("World"), endOfLine: []byte("\r\n")},
+		{line: []byte("AnotherLine"), endOfLine: []byte("")},
 	}
 
-	for _, tt := range tl {
-		t.Run(tt.n, func(t *testing.T) {
-			if err := returnSendError(tt.r, tt.te); err != nil {
-				exp := &SendError{Reason: tt.r, isTemp: tt.te}
-				if !errors.Is(err, exp) {
-					t.Errorf("error mismatch, expected: %s (temp: %t), got: %s (temp: %t)", tt.r, tt.te,
-						exp.Error(), exp.isTemp)
-				}
-				if !strings.Contains(fmt.Sprintf("%s", err), tt.r.String()) {
-					t.Errorf("error string mismatch, expected: %s, got: %s",
-						tt.r.String(), fmt.Sprintf("%s", err))
-				}
-			}
-		})
+	result := ls.splitLine([]byte("\r\n"))
+	if len(result) != len(expected) {
+		t.Errorf("Expected %d lines, but got %d", len(expected), len(result))
+	}
+
+	for i := range result {
+		if !bytes.Equal(result[i].line, expected[i].line) || !bytes.Equal(result[i].endOfLine, expected[i].endOfLine) {
+			t.Errorf("Line %d mismatch. Expected line: %s, endOfLine: %s, got line: %s, endOfLine: %s",
+				i, expected[i].line, expected[i].endOfLine, result[i].line, result[i].endOfLine)
+		}
 	}
 }
+
+// FuzzSplitLine tests the parseLsplitLineines method with fuzzing
+func FuzzSplitLine(f *testing.F) {
+	f.Add([]byte("Hello\r\nWorld"), []byte("\r\n"))
+	f.Fuzz(func(t *testing.T, input, sep []byte) {
+		ls := lines{
+			{line: input, endOfLine: []byte("")},
+		}
+		_ = ls.splitLine(sep)
+	})
+}