问为什么在控制台应用程序中使用SendGrid C#客户端库发送电子邮件时需要使用Wait

EN

static void Main(string[] args) {
    //var customerImport = new CustomerImport();
    //customerImport.DoImport();

    var mailClient = new MailClient();
    var recipients = new List<string>();
    recipients.Add("test@lobbycentral.com");

    //Never sends an email
    var response = mailClient.SendMail("noreply@lobbycentral.com", recipients, "Test email", "This is a test of the new SG client", false);

    //Will send an email
    mailClient.SendMail("noreply@lobbycentral.com", recipients, "Test email", "This is a test of the new SG client", false).Wait();
}

public async Task SendMail(string emailFrom, List<string> emailTo, string subject, string body, bool isPlainText) {

    try {
        var apiKey = Utils.GetConfigValue("sendgridAPIKey");
        var emails = new List<EmailAddress>();

        foreach (string email in emailTo) {
            emails.Add(new EmailAddress(email));
        }

        var plainTextContent = "";
        var htmlContent = "";

        if (!isPlainText) {
            htmlContent = body;
        } else {
            plainTextContent = body;
        }

        var message = MailHelper.CreateSingleEmailToMultipleRecipients(new EmailAddress(emailFrom, "LobbyCentral"), emails, subject, plainTextContent, htmlContent);

        //if (metaData != null)
        //    message.AddCustomArgs(metaData);

        foreach (string filename in FileAttachments) {
            if (System.IO.File.Exists(filename)) {
                using (var filestream = System.IO.File.OpenRead(filename)) {
                    await message.AddAttachmentAsync(filename, filestream);
                }
            }
        }

        foreach (PlainTextAttachmentM plainTextM in PlainTextAttachments) {
            byte[] byteData = Encoding.ASCII.GetBytes(plainTextM.Content);

            var attachment = new Attachment();
            attachment.Content = Convert.ToBase64String(byteData);
            attachment.Filename = plainTextM.AttachmentFilename;
            attachment.Type = "txt/plain";
            attachment.Disposition = "attachment";

            message.AddAttachment(attachment);
        }
        
        var client = new SendGridClient(apiKey);
        var response = await client.SendEmailAsync(message);

        if (response.IsSuccessStatusCode) {

            if (DeleteAttachmentsAfterSend && FileAttachments.Count > 0) {
                foreach (string filename in FileAttachments) {
                    if (System.IO.File.Exists(filename)) {
                        System.IO.File.Delete(filename);
                    }
                }
            }
        } else {
            Utils.DebugPrint("error sending email");
        }


    } catch (Exception ex) {
        throw new Exception(string.Format("{0}.{1}: {2} {3}", System.Reflection.MethodBase.GetCurrentMethod().DeclaringType.FullName, System.Reflection.MethodBase.GetCurrentMethod().Name, ex.Message, ex.StackTrace));
    }
}