diff --git a/admin_setting_smtp.go b/admin_setting_smtp.go
index 5afc98d72..679fc0c99 100644
--- a/admin_setting_smtp.go
+++ b/admin_setting_smtp.go
@@ -97,9 +97,12 @@ func (a *adminSMTPSettings) Update(ctx context.Context, options AdminSMTPSetting
 }
 
 func (o AdminSMTPSettingsUpdateOptions) valid() error {
-	_, isValidType := validSMTPAuthType[*o.Auth]
-	if !isValidType {
-		return ErrInvalidSMTPAuth
+	if validString((*string)(o.Auth)) {
+		_, isValidType := validSMTPAuthType[*o.Auth]
+		if !isValidType {
+			return ErrInvalidSMTPAuth
+		}
 	}
+
 	return nil
 }
diff --git a/admin_setting_smtp_integration_test.go b/admin_setting_smtp_integration_test.go
index 1c337b6f1..1cbba14b3 100644
--- a/admin_setting_smtp_integration_test.go
+++ b/admin_setting_smtp_integration_test.go
@@ -36,11 +36,23 @@ func TestAdminSettings_SMTP_Update(t *testing.T) {
 	ctx := context.Background()
 
 	enabled := false
-	smtpSettings, err := client.Admin.Settings.SMTP.Update(ctx, AdminSMTPSettingsUpdateOptions{
-		Enabled: Bool(enabled),
-		Auth:    SMTPAuthValue(SMTPAuthNone),
-	})
 
-	require.NoError(t, err)
-	assert.Equal(t, enabled, smtpSettings.Enabled)
+	t.Run("with Auth option defined", func(t *testing.T) {
+		smtpSettings, err := client.Admin.Settings.SMTP.Update(ctx, AdminSMTPSettingsUpdateOptions{
+			Enabled: Bool(enabled),
+			Auth:    SMTPAuthValue(SMTPAuthNone),
+		})
+
+		require.NoError(t, err)
+		assert.Equal(t, enabled, smtpSettings.Enabled)
+	})
+	t.Run("with no Auth option", func(t *testing.T) {
+		smtpSettings, err := client.Admin.Settings.SMTP.Update(ctx, AdminSMTPSettingsUpdateOptions{
+			Enabled: Bool(enabled),
+		})
+
+		require.NoError(t, err)
+		assert.Equal(t, SMTPAuthNone, smtpSettings.Auth)
+		assert.Equal(t, enabled, smtpSettings.Enabled)
+	})
 }