diff --git a/client.go b/client.go
index 2a20c96..14a3c03 100644
--- a/client.go
+++ b/client.go
@@ -246,8 +246,12 @@ func (c *Client) SetTLSPolicy(p TLSPolicy) {
 }
 
 // SetTLSConfig overrides the current *tls.Config with the given *tls.Config value
-func (c *Client) SetTLSConfig(co *tls.Config) {
+func (c *Client) SetTLSConfig(co *tls.Config) error {
+	if co == nil {
+		return ErrInvalidTLSConfig
+	}
 	c.tlsconfig = co
+	return nil
 }
 
 // SetUsername overrides the current username string with the given value
diff --git a/client_test.go b/client_test.go
index e4e874f..132382f 100644
--- a/client_test.go
+++ b/client_test.go
@@ -2,6 +2,7 @@ package mail
 
 import (
 	"crypto/tls"
+	"fmt"
 	"net/smtp"
 	"testing"
 	"time"
@@ -50,6 +51,10 @@ func TestNewClient(t *testing.T) {
 				t.Errorf("failed to create new client. TLS config min versino expected: %d, got: %d",
 					DefaultTLSMinVersion, c.tlsconfig.MinVersion)
 			}
+			if c.ServerAddr() != fmt.Sprintf("%s:%d", tt.host, c.port) {
+				t.Errorf("failed to create new client. c.ServerAddr() expected: %s, got: %s",
+					fmt.Sprintf("%s:%d", tt.host, c.port), c.ServerAddr())
+			}
 		})
 	}
 }
@@ -69,6 +74,7 @@ func TestNewClientWithOptions(t *testing.T) {
 		{"WithTimeout()", WithTimeout(-10), true},
 		{"WithSSL()", WithSSL(), false},
 		{"WithHELO()", WithHELO(host), false},
+		{"WithHELO(); helo is empty", WithHELO(""), true},
 		{"WithTLSPolicy()", WithTLSPolicy(TLSOpportunistic), false},
 		{"WithTLSConfig()", WithTLSConfig(&tls.Config{}), false},
 		{"WithTLSConfig(); config is nil", WithTLSConfig(nil), true},
@@ -120,14 +126,17 @@ func TestWithPort(t *testing.T) {
 		name  string
 		value int
 		want  int
+		sf    bool
 	}{
-		{"set port to 25", 25, 25},
-		{"set port to 465", 465, 465},
+		{"set port to 25", 25, 25, false},
+		{"set port to 465", 465, 465, false},
+		{"set port to 100000", 100000, 25, true},
+		{"set port to -10", -10, 25, true},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			c, err := NewClient(DefaultHost, WithPort(tt.value))
-			if err != nil {
+			if err != nil && !tt.sf {
 				t.Errorf("failed to create new client: %s", err)
 				return
 			}
@@ -144,15 +153,17 @@ func TestWithTimeout(t *testing.T) {
 		name  string
 		value time.Duration
 		want  time.Duration
+		sf    bool
 	}{
-		{"set timeout to 5s", time.Second * 5, time.Second * 5},
-		{"set timeout to 30s", time.Second * 30, time.Second * 30},
-		{"set timeout to 1m", time.Minute, time.Minute},
+		{"set timeout to 5s", time.Second * 5, time.Second * 5, false},
+		{"set timeout to 30s", time.Second * 30, time.Second * 30, false},
+		{"set timeout to 1m", time.Minute, time.Minute, false},
+		{"set timeout to 0", 0, DefaultTimeout, true},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			c, err := NewClient(DefaultHost, WithTimeout(tt.value))
-			if err != nil {
+			if err != nil && !tt.sf {
 				t.Errorf("failed to create new client: %s", err)
 				return
 			}
@@ -163,47 +174,27 @@ func TestWithTimeout(t *testing.T) {
 	}
 }
 
-// TestWithSSL tests the WithSSL() option for the NewClient() method
-func TestWithSSL(t *testing.T) {
-	tests := []struct {
-		name string
-		want bool
-	}{
-		{"set SSL to true", true},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			c, err := NewClient(DefaultHost, WithSSL())
-			if err != nil {
-				t.Errorf("failed to create new client: %s", err)
-				return
-			}
-			if c.ssl != tt.want {
-				t.Errorf("failed to set SSL. Want: %t, got: %t", tt.want, c.ssl)
-			}
-		})
-	}
-}
-
 // TestWithTLSPolicy tests the WithTLSPolicy() option for the NewClient() method
 func TestWithTLSPolicy(t *testing.T) {
 	tests := []struct {
 		name  string
 		value TLSPolicy
-		want  TLSPolicy
+		want  string
+		sf    bool
 	}{
-		{"Policy: TLSMandatory", TLSMandatory, TLSMandatory},
-		{"Policy: TLSOpportunistic", TLSOpportunistic, TLSOpportunistic},
-		{"Policy: NoTLS", NoTLS, NoTLS},
+		{"Policy: TLSMandatory", TLSMandatory, TLSMandatory.String(), false},
+		{"Policy: TLSOpportunistic", TLSOpportunistic, TLSOpportunistic.String(), false},
+		{"Policy: NoTLS", NoTLS, NoTLS.String(), false},
+		{"Policy: Invalid", -1, "UnknownPolicy", true},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			c, err := NewClient(DefaultHost, WithTLSPolicy(tt.value))
-			if err != nil {
+			if err != nil && !tt.sf {
 				t.Errorf("failed to create new client: %s", err)
 				return
 			}
-			if c.tlspolicy != tt.want {
+			if c.tlspolicy.String() != tt.want {
 				t.Errorf("failed to set TLSPolicy. Want: %s, got: %s", tt.want, c.tlspolicy)
 			}
 		})
@@ -215,11 +206,13 @@ func TestSetTLSPolicy(t *testing.T) {
 	tests := []struct {
 		name  string
 		value TLSPolicy
-		want  TLSPolicy
+		want  string
+		sf    bool
 	}{
-		{"Policy: TLSMandatory", TLSMandatory, TLSMandatory},
-		{"Policy: TLSOpportunistic", TLSOpportunistic, TLSOpportunistic},
-		{"Policy: NoTLS", NoTLS, NoTLS},
+		{"Policy: TLSMandatory", TLSMandatory, TLSMandatory.String(), false},
+		{"Policy: TLSOpportunistic", TLSOpportunistic, TLSOpportunistic.String(), false},
+		{"Policy: NoTLS", NoTLS, NoTLS.String(), false},
+		{"Policy: Invalid", -1, "UnknownPolicy", true},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -229,7 +222,7 @@ func TestSetTLSPolicy(t *testing.T) {
 				return
 			}
 			c.SetTLSPolicy(tt.value)
-			if c.tlspolicy != tt.want {
+			if c.tlspolicy.String() != tt.want {
 				t.Errorf("failed to set TLSPolicy. Want: %s, got: %s", tt.want, c.tlspolicy)
 			}
 		})