Send email with WPF Console on C#

Question

I'm trying to build a WPF Application on C# (.NET 6.0). This app has to send mail. I give as parameters: mailFrom, mailTo, host, password, subject and the message's body. The class which responds to the button 'Send' is this:

public partial class MainWindow : Window
{
    private readonly ILogger<MainWindow> _logger;

    public MainWindow()
    {
        InitializeComponent();
    }

    public MainWindow(ILogger<MainWindow> logger) : this()
    {
        _logger = logger;
    }

    private void btnSender_Click(object sender, RoutedEventArgs e)
    {
        MessageRequest mailRequest = new MessageRequest();

        var builder = new BodyBuilder();

        mailRequest.ToEmail = tbReceiver.Text;
        mailRequest.FromEmail = tbSender.Text;
        mailRequest.Subject = tbSubject.Text;
        mailRequest.Body = tbMessage.Text;
        mailRequest.Host = tbHost.Text;

        SendMail(mailRequest, builder);
    }

    private void SendMail(MessageRequest mailRequest, BodyBuilder builder)
    {
        var email = new MimeMessage();

        email.From.Add(MailboxAddress.Parse(mailRequest.FromEmail));
        email.To.Add(MailboxAddress.Parse(mailRequest.ToEmail));
        email.Subject = mailRequest.Subject;
        email.Sender = MailboxAddress.Parse(mailRequest.FromEmail);

        builder.HtmlBody = mailRequest.Body;
        email.Body = builder.ToMessageBody();

        using var smtp = new SmtpClient();

        smtp.CheckCertificateRevocation = false;

        smtp.Connected += Smtp_Connected;
        smtp.Authenticated += Smtp_Authenticated;
        smtp.Disconnected += Smtp_Disconnected;
        smtp.MessageSent += Smtp_MessageSent;

        if (!IsValidEmail(email.From.ToString()) || !IsValidEmail(email.To.ToString()))
        {
            _logger.LogError("ERROR: Mail not valid.");
        }
        else
        {
            smtp.Connect(mailRequest.Host, 587, SecureSocketOptions.StartTls);

            if (true)
            {
                smtp.Authenticate(email.From.ToString(), "XXX");
            }

            smtp.Send(email);
        }            

        smtp.Disconnect(true);
    }

    private void Smtp_MessageSent(object? sender, MessageSentEventArgs e)
    {
        _logger.LogTrace("Message sent {message}. Response: {response}", e.Message, e.Response);
    }

    private void Smtp_Disconnected(object? sender, DisconnectedEventArgs e)
    {
        _logger.LogTrace("Disconnected to SMTP {host}", e.Host);

    }

    private void Smtp_Authenticated(object? sender, AuthenticatedEventArgs e)
    {
        _logger.LogTrace("Authenticated to SMTP host");
    }

    private void Smtp_Connected(object? sender, ConnectedEventArgs e)
    {
        _logger.LogTrace("Connected to SMTP {host}", e.Host);
    }
    private bool IsValidEmail(string email)
    {
        try
        {
            var mailAddress = new System.Net.Mail.MailAddress(email);
            return mailAddress.Address == email;
        }
        catch
        {
            return false;
        }
    }
}

but it returns this error: 'System.ArgumentNullException: 'Value cannot be null. Arg_ParamName_Name'. I find that the problem is the logger which doesn't work and return this error. I comment the lines of code: smtp.Connected += Smtp_Connected; smtp.Authenticated += Smtp_Authenticated; smtp.Disconnected += Smtp_Disconnected; smtp.MessageSent += Smtp_MessageSent;

and now it works. But if I write the same code but only for an Web API it works also if I don't comment these lines. What could be the solution?