收件人电子邮件地址重叠

Question

I recently deployed a C# script that utilizes System.Net.Mail functionality. The mailing system will work by sending a photobooth screenshot as an attachment to each respective email addresses once users filled up the form ( hence each users are supposed to receive an unique image attachments ).

The script works flawlessly but I am suffering from one issue: once the internet connection became slow or suffer from some random down time, the email addresses will overlap and current guests will receive attachments from previous users.

I am wondering if there are any method that can create/compose a new mail without interrupting the current sending processes. I am using Gmail btw.

Below is the code I'm using:

MailMessage mail = new MailMessage();

mail.Attachments.Clear();

mail.From = new MailAddress("@gmail.com");
mail.To.Add(email);
mail.Subject = "";
mail.Body = "";

mail.Attachments.Add(new Attachment("screenshot.jpg"));
//mail.Attachments.Add (new Attachment("screenshot.jpg"));

SmtpClient smtpServer = new SmtpClient("smtp.gmail.com");
smtpServer.Port = 587;
smtpServer.Credentials = new System.Net.NetworkCredential("@gmail.com", "") as ICredentialsByHost;
smtpServer.EnableSsl = true;
ServicePointManager.ServerCertificateValidationCallback = 
    delegate(object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
{
    return true;
};
smtpServer.Send(mail);
//Debug.Log("success");
sent = true;

Answer 1

Best solution would be to decouple the processes of creating and sending the emails.

Create each mail message and drop it in a queue. You can then have the mail sending process monitoring the queue and delivering any messages there as quickly as it can.

Answer 2

在单独的线程上发送邮件，例如使用任务。

    Task.Factory.StartNew(() => smtpServer.Send(mail));

Answer 3

This is a web application, correct? And is this line of code pulling from a physical file on the disk?:

mail.Attachments.Add (new Attachment ("screenshot.jpg"));

If so then there's your problem. Web applications are multi-threaded. So lots of users could be modifying that file at the same time. In the time it takes the application to go from the step of modifying that file to the step of reading that file, another user may have modified it.

You have a couple of options:

1. Create a unique file name for each time a user goes through this process. Do you need to keep the files afterward? I'm guessing not, since you overwrite them. So use something like Path.GetTempFileName() to create a temporary file and pass that from the saving step to the reading/emailing step instead of hard-coding the same file name.
2. Never save the file to disk, and instead just pass the byte[] of the file's data from the uploading step to the sending step, building the Attachment from the byte array .