Recently I had to send an email blast out to about two thousand email subscribers from a client's ASP.NET Web Forms application. The client had an admin form where they would compose and send out the email. Unfortunately, with that many emails the Web form would inevitably hang. Plus, with Exchange Server there is no easy way to know how many emails actually got sent; you could use Powershell to determine this or you could log it but it still isn't a robust way of doing things.
The conventional wisdom is to use a third party service for mass mailings and most times this is probably your best option. In this situation, an email blast is only sent every 5 years so it really didn't make sense to enrol in a monthly plan. With a little due diligence, this can be accomplished with a very simple console application which can be called from the Web form to dispatch the emails.
The basic design is that the subject line and email body text are entered in the form and passed to the console application as string parameters. In the console app, we can obtain the email addresses from a database and send the emails out in batches with a pause between each batch.
Some basics first: the entry point to any console application is the Main method:
// Mailer class in console application
static void Main(string[] args)
{
if (args.Length >= 2)
{
SmtpClient smtpClient = new SmtpClient(EMAIL_HOST);
smtpClient.Host = "localhost";
MailMessage message = new MailMessage();
message.Priority = MailPriority.High;
message.Subject = args[0];
message.Body = args[1];
smtpClient.Send(FROM_ADDRESS, TO_ADDRESS, message.Subject, message.Body);
}
}
The array of strings args parameter corresponds directly to the command line parameters passed to the console application; string[0] is the first parameter, strg[1] is the second parameter and so on. This is different in C and C++, where the name of the console application itself is the first parameter... when in doubt, try it out!
Note that when testing this on the command line initially, that there is a limitation on the size of the strings you can pass. This will not apply when sending the parameters programmatically from the Web form code-behind. You can test that your console app is sending emails by creating a drop folder on your C drive. Download and install Live Mail to view the .eml files generated. You can create a dummy gmail account to get this running and choose not to make Live Mail your default email client during the install (if this is your preference). This is a really simple and useful way to test email functionality locally on your dev machine. Just update your Web.Config file with the following to get it working:
<system.net>
<mailSettings>
<smtp deliveryMethod="SpecifiedPickupDirectory">
<specifiedPickupDirectory pickupDirectoryLocation="c:\maildrop" />
</smtp>
</mailSettings>
</system.net>
To generate a test email with the console app and pass the subject and body parameters, call it like this:
// DOS command line
C:\>ConsoleApplication1 "Subject Line Text" "Some body text"
To call the console app from the Web form code-behind we use the Process.Start method. We can avail of the ProcessStartInfo class to set up any properties in advance of making the process call.
// Web form code-behind
// Pass subject and message strings as params to console app
ProcessStartInfo info = new ProcessStartInfo();
string arguments = String.Format(@"""{0}"" ""{1}""",
subjectText.Text.Replace(@"""", @""""""),
messageText.Text.Replace(@"""", @""""""));
info.FileName = MAILER_FILEPATH;
info.Arguments = arguments;
Process.Start(info);
We also need to take account of the possibility of quotes being included in the subject line or body text. I enlisted some help on this issue with a StackOverflow question. The solution was a combination of composite string formatting and verbatim "@" string literals. See the String.Format call in the code snippet above.
If you've been testing the console app and then go on to debugging with VS, you may come up against a file locking issue. This issue is a known bug - I've seen bug reports going back to 2006 on this one.
Error 9 Unable to copy file "obj\x86\Debug\ConsoleApplication1.exe" to "bin \Debug\ConsoleApplication1.exe". The process cannot access the file 'bin\Debug\ConsoleApplication1.exe' because it is being used by another process.
There are two workarounds to this. My way is to close out VS and then kill any remaining processes for the console app: Windows Task Manager -> Processes tab -> Show processes from all users -> right- click each process and kill it (End Process). The second method is to add a pre-build script.