diff --git a/client.go b/client.go
index 6b9baf1..b93e53b 100644
--- a/client.go
+++ b/client.go
@@ -511,10 +511,15 @@ func (c *Client) DialWithContext(pc context.Context) error {
 		return err
 	}
 
-	c.sc, err = smtp.NewClient(c.co, c.host)
+	sc, err := smtp.NewClient(c.co, c.host)
 	if err != nil {
 		return err
 	}
+	if sc == nil {
+		return fmt.Errorf("SMTP client is nil")
+	}
+	c.sc = sc
+
 	if c.l != nil {
 		c.sc.SetLogger(c.l)
 	}
diff --git a/msg.go b/msg.go
index e623958..dbce277 100644
--- a/msg.go
+++ b/msg.go
@@ -287,7 +287,9 @@ func (m *Msg) SetAddrHeader(h AddrHeader, v ...string) error {
 	}
 	switch h {
 	case HeaderFrom:
-		m.addrHeader[h] = []*mail.Address{al[0]}
+		if len(al) > 0 {
+			m.addrHeader[h] = []*mail.Address{al[0]}
+		}
 	default:
 		m.addrHeader[h] = al
 	}
@@ -518,7 +520,9 @@ func (m *Msg) RequestMDNTo(t ...string) error {
 		}
 		tl = append(tl, a.String())
 	}
-	m.genHeader[HeaderDispositionNotificationTo] = tl
+	if _, ok := m.genHeader[HeaderDispositionNotificationTo]; ok {
+		m.genHeader[HeaderDispositionNotificationTo] = tl
+	}
 	return nil
 }
 
@@ -539,7 +543,9 @@ func (m *Msg) RequestMDNAddTo(t string) error {
 	var tl []string
 	tl = append(tl, m.genHeader[HeaderDispositionNotificationTo]...)
 	tl = append(tl, a.String())
-	m.genHeader[HeaderDispositionNotificationTo] = tl
+	if _, ok := m.genHeader[HeaderDispositionNotificationTo]; ok {
+		m.genHeader[HeaderDispositionNotificationTo] = tl
+	}
 	return nil
 }
 
@@ -591,8 +597,8 @@ func (m *Msg) GetAddrHeader(h AddrHeader) []*mail.Address {
 // GetAddrHeaderString returns the address string of the requested address header of the Msg
 func (m *Msg) GetAddrHeaderString(h AddrHeader) []string {
 	var al []string
-	for i := range m.addrHeader[h] {
-		al = append(al, m.addrHeader[h][i].String())
+	for _, mh := range m.addrHeader[h] {
+		al = append(al, mh.String())
 	}
 	return al
 }
@@ -999,9 +1005,12 @@ func (m *Msg) WriteToSendmailWithContext(ctx context.Context, sp string, a ...st
 	if err != nil {
 		return fmt.Errorf("failed to set STDIN pipe: %w", err)
 	}
+	if se == nil || si == nil {
+		return fmt.Errorf("received nil for STDERR or STDIN pipe")
+	}
 
 	// Start the execution and write to STDIN
-	if err := ec.Start(); err != nil {
+	if err = ec.Start(); err != nil {
 		return fmt.Errorf("could not start sendmail execution: %w", err)
 	}
 	_, err = m.WriteTo(si)
@@ -1012,7 +1021,7 @@ func (m *Msg) WriteToSendmailWithContext(ctx context.Context, sp string, a ...st
 	}
 
 	// Close STDIN and wait for completion or cancellation of the sendmail executable
-	if err := si.Close(); err != nil {
+	if err = si.Close(); err != nil {
 		return fmt.Errorf("failed to close STDIN pipe: %w", err)
 	}
 
@@ -1025,7 +1034,7 @@ func (m *Msg) WriteToSendmailWithContext(ctx context.Context, sp string, a ...st
 		return fmt.Errorf("sendmail command failed: %s", string(serr))
 	}
 
-	if err := ec.Wait(); err != nil {
+	if err = ec.Wait(); err != nil {
 		return fmt.Errorf("sendmail command execution failed: %w", err)
 	}
 
@@ -1069,7 +1078,7 @@ func (m *Msg) HasSendError() bool {
 // corresponding error was of temporary nature and should be retried later
 func (m *Msg) SendErrorIsTemp() bool {
 	var e *SendError
-	if errors.As(m.sendError, &e) {
+	if errors.As(m.sendError, &e) && e != nil {
 		return e.isTemp
 	}
 	return false
diff --git a/msg_test.go b/msg_test.go
index 14e5f18..47d5b18 100644
--- a/msg_test.go
+++ b/msg_test.go
@@ -216,6 +216,9 @@ func (mw uppercaseMiddleware) Handle(m *Msg) *Msg {
 	if !ok {
 		fmt.Println("can't find the subject header")
 	}
+	if s == nil || len(s) < 1 {
+		s = append(s, "")
+	}
 	m.Subject(strings.ToUpper(s[0]))
 	return m
 }
@@ -231,6 +234,9 @@ func (mw encodeMiddleware) Handle(m *Msg) *Msg {
 	if !ok {
 		fmt.Println("can't find the subject header")
 	}
+	if s == nil || len(s) < 1 {
+		s = append(s, "")
+	}
 	m.Subject(strings.Replace(s[0], "a", "@", -1))
 	return m
 }
@@ -752,7 +758,9 @@ func TestMsg_SetMessageIDWithValue(t *testing.T) {
 		t.Errorf("SetMessageID() failed. Expected value, got: empty")
 		return
 	}
-	m.genHeader[HeaderMessageID] = nil
+	if _, ok := m.genHeader[HeaderMessageID]; ok {
+		m.genHeader[HeaderMessageID] = nil
+	}
 	v := "This.is.a.message.id"
 	vf := "<This.is.a.message.id>"
 	m.SetMessageIDWithValue(v)
@@ -773,7 +781,9 @@ func TestMsg_SetMessageIDRandomness(t *testing.T) {
 		m := NewMsg()
 		m.SetMessageID()
 		mid := m.GetGenHeader(HeaderMessageID)
-		mids = append(mids, mid[0])
+		if len(mid) > 0 {
+			mids = append(mids, mid[0])
+		}
 	}
 	c := make(map[string]int)
 	for i := range mids {
@@ -1125,9 +1135,11 @@ func TestMsg_RequestMDN(t *testing.T) {
 	if err := m.RequestMDNTo(v); err != nil {
 		t.Errorf("RequestMDNTo with a single valid address failed: %s", err)
 	}
-	if m.genHeader[HeaderDispositionNotificationTo][0] != fmt.Sprintf("<%s>", v) {
-		t.Errorf("RequestMDNTo with a single valid address failed. Expected: %s, got: %s", v,
-			m.genHeader[HeaderDispositionNotificationTo][0])
+	if val := m.genHeader[HeaderDispositionNotificationTo]; len(val) > 1 {
+		if val[0] != fmt.Sprintf("<%s>", v) {
+			t.Errorf("RequestMDNTo with a single valid address failed. Expected: %s, got: %s", v,
+				val[0])
+		}
 	}
 	m.Reset()
 
@@ -1135,13 +1147,17 @@ func TestMsg_RequestMDN(t *testing.T) {
 	if err := m.RequestMDNTo(vl...); err != nil {
 		t.Errorf("RequestMDNTo with a multiple valid address failed: %s", err)
 	}
-	if m.genHeader[HeaderDispositionNotificationTo][0] != fmt.Sprintf("<%s>", v) {
-		t.Errorf("RequestMDNTo with a multiple valid addresses failed. Expected 0: %s, got 0: %s", v,
-			m.genHeader[HeaderDispositionNotificationTo][0])
+	if val := m.genHeader[HeaderDispositionNotificationTo]; len(val) > 0 {
+		if val[0] != fmt.Sprintf("<%s>", v) {
+			t.Errorf("RequestMDNTo with a multiple valid addresses failed. Expected 0: %s, got 0: %s", v,
+				val[0])
+		}
 	}
-	if m.genHeader[HeaderDispositionNotificationTo][1] != fmt.Sprintf("<%s>", v2) {
-		t.Errorf("RequestMDNTo with a multiple valid addresses failed. Expected 1: %s, got 1: %s", v2,
-			m.genHeader[HeaderDispositionNotificationTo][1])
+	if val := m.genHeader[HeaderDispositionNotificationTo]; len(val) > 1 {
+		if val[1] != fmt.Sprintf("<%s>", v2) {
+			t.Errorf("RequestMDNTo with a multiple valid addresses failed. Expected 1: %s, got 1: %s", v2,
+				val[1])
+		}
 	}
 	m.Reset()
 
@@ -1158,9 +1174,11 @@ func TestMsg_RequestMDN(t *testing.T) {
 	if err := m.RequestMDNAddTo(v2); err != nil {
 		t.Errorf("RequestMDNAddTo with a valid address failed: %s", err)
 	}
-	if m.genHeader[HeaderDispositionNotificationTo][1] != fmt.Sprintf("<%s>", v2) {
-		t.Errorf("RequestMDNTo with a multiple valid addresses failed. Expected 1: %s, got 1: %s", v2,
-			m.genHeader[HeaderDispositionNotificationTo][1])
+	if val := m.genHeader[HeaderDispositionNotificationTo]; len(val) > 1 {
+		if val[1] != fmt.Sprintf("<%s>", v2) {
+			t.Errorf("RequestMDNTo with a multiple valid addresses failed. Expected 1: %s, got 1: %s", v2,
+				val[1])
+		}
 	}
 	m.Reset()
 
@@ -1168,16 +1186,20 @@ func TestMsg_RequestMDN(t *testing.T) {
 	if err := m.RequestMDNToFormat(n, v); err != nil {
 		t.Errorf("RequestMDNToFormat with a single valid address failed: %s", err)
 	}
-	if m.genHeader[HeaderDispositionNotificationTo][0] != fmt.Sprintf(`"%s" <%s>`, n, v) {
-		t.Errorf(`RequestMDNToFormat with a single valid address failed. Expected: "%s" <%s>, got: %s`, n, v,
-			m.genHeader[HeaderDispositionNotificationTo][0])
+	if val := m.genHeader[HeaderDispositionNotificationTo]; len(val) > 0 {
+		if val[0] != fmt.Sprintf(`"%s" <%s>`, n, v) {
+			t.Errorf(`RequestMDNToFormat with a single valid address failed. Expected: "%s" <%s>, got: %s`, n, v,
+				val[0])
+		}
 	}
 	if err := m.RequestMDNAddToFormat(n2, v2); err != nil {
 		t.Errorf("RequestMDNAddToFormat with a valid address failed: %s", err)
 	}
-	if m.genHeader[HeaderDispositionNotificationTo][1] != fmt.Sprintf(`"%s" <%s>`, n2, v2) {
-		t.Errorf(`RequestMDNAddToFormat with a single valid address failed. Expected: "%s" <%s>, got: %s`, n2, v2,
-			m.genHeader[HeaderDispositionNotificationTo][1])
+	if val := m.genHeader[HeaderDispositionNotificationTo]; len(val) > 1 {
+		if val[1] != fmt.Sprintf(`"%s" <%s>`, n2, v2) {
+			t.Errorf(`RequestMDNAddToFormat with a single valid address failed. Expected: "%s" <%s>, got: %s`, n2, v2,
+				val[1])
+		}
 	}
 	m.Reset()
 
@@ -2567,6 +2589,10 @@ func TestMsg_WriteToFile(t *testing.T) {
 	if err != nil {
 		t.Errorf("failed to stat output file: %s", err)
 	}
+	if fi == nil {
+		t.Errorf("received empty file handle")
+		return
+	}
 	if fi.Size() <= 0 {
 		t.Errorf("output file is expected to contain data but its size is zero")
 	}
diff --git a/msgwriter.go b/msgwriter.go
index 2b29035..cbf0a8f 100644
--- a/msgwriter.go
+++ b/msgwriter.go
@@ -67,13 +67,13 @@ func (mw *msgWriter) writeMsg(m *Msg) {
 	// Set the FROM header (or envelope FROM if FROM is empty)
 	hf := true
 	f, ok := m.addrHeader[HeaderFrom]
-	if !ok || len(f) == 0 {
+	if !ok || (len(f) == 0 || f == nil) {
 		f, ok = m.addrHeader[HeaderEnvelopeFrom]
-		if !ok || len(f) == 0 {
+		if !ok || (len(f) == 0 || f == nil) {
 			hf = false
 		}
 	}
-	if hf {
+	if hf && (len(f) > 0 && f[0] != nil) {
 		mw.writeHeader(Header(HeaderFrom), f[0].String())
 	}
 
diff --git a/reader.go b/reader.go
index ee74f7d..acde0a2 100644
--- a/reader.go
+++ b/reader.go
@@ -25,7 +25,7 @@ func (r *Reader) Read(p []byte) (n int, err error) {
 	if r.err != nil {
 		return 0, r.err
 	}
-	if r.empty() {
+	if r.empty() || r.buf == nil {
 		r.Reset()
 		if len(p) == 0 {
 			return 0, nil
diff --git a/reader_test.go b/reader_test.go
index 3f30735..c1c198b 100644
--- a/reader_test.go
+++ b/reader_test.go
@@ -6,7 +6,9 @@ package mail
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
+	"io"
 	"testing"
 )
 
@@ -64,9 +66,20 @@ func TestReader_Read_error(t *testing.T) {
 // TestReader_Read_empty tests the Reader.Read method with an empty buffer
 func TestReader_Read_empty(t *testing.T) {
 	r := Reader{buf: []byte{}}
-	var p []byte
+	p := make([]byte, 1)
+	p[0] = 'a'
 	_, err := r.Read(p)
-	if err != nil {
+	if err != nil && !errors.Is(err, io.EOF) {
+		t.Errorf("Reader failed: %s", err)
+	}
+}
+
+// TestReader_Read_nil tests the Reader.Read method with a nil buffer
+func TestReader_Read_nil(t *testing.T) {
+	r := Reader{buf: nil, off: -10}
+	p := make([]byte, 0)
+	_, err := r.Read(p)
+	if err != nil && !errors.Is(err, io.EOF) {
 		t.Errorf("Reader failed: %s", err)
 	}
 }
diff --git a/senderror.go b/senderror.go
index b3a8a7b..34037d1 100644
--- a/senderror.go
+++ b/senderror.go
@@ -98,7 +98,7 @@ func (e *SendError) Error() string {
 // Is implements the errors.Is functionality and compares the SendErrReason
 func (e *SendError) Is(et error) bool {
 	var t *SendError
-	if errors.As(et, &t) {
+	if errors.As(et, &t) && t != nil {
 		return e.Reason == t.Reason && e.isTemp == t.isTemp
 	}
 	return false
@@ -106,6 +106,9 @@ func (e *SendError) Is(et error) bool {
 
 // IsTemp returns true if the delivery error is of temporary nature and can be retried
 func (e *SendError) IsTemp() bool {
+	if e == nil {
+		return false
+	}
 	return e.isTemp
 }