I am using the Postmark library for .Net:

public async Task SendAsync(string toEmail, string subject, string textBody, string? htmlBody = null)
{
    var message = new PostmarkMessage()
    {
        To = toEmail,
        From = "",
        Subject = subject,
        TextBody = textBody,
        HtmlBody = htmlBody ?? $"
{textBody}
",
        MessageStream = "",
        TrackOpens = false
    };

    var client = new PostmarkClient(configuration["Postmark:Token"]);
    var sendResult = await client.SendMessageAsync(message);

    Console.WriteLine(System.Text.Json.JsonSerializer.Serialize(sendResult));
    // Returning this:
    // {"MessageID":"7474ea9e-a72b-4af5-9a71-5be460b7dd8c","Status":0,"Message":"OK","SubmittedAt":"2025-12-13T12:16:57.6070079+01:00","To":xxxxxx@gmail.com","ErrorCode":0}

    if (sendResult.Status == PostmarkStatus.Success)
    {
        return new MailResult { Succeeded = true };
    }
    else
    {
        Console.WriteLine($"Error sending email: {sendResult.Message}");
        return new MailResult { Succeeded = false, Error = "Failed to send email. Check logs for more details" };
    }
}

Everything seems to be successfull, I event provided the Object returned by SendMessageAsync, but nothing appear in my Stream activity.

Please help, I am becoming crazy with that.