VerySimple

Attaching files to emails in .NET is easy if you’ve physically saved the file on the server. What if you don’t want to save the file, though? It’s actually pretty simple as well, but you need to convert the data to be attached into a Stream.

The following code converts some plain old text into a MemoryStream and then attaches it to an email message as a .txt file. The same can be done with any other type of data, you just need the appropriate MemoryStream.

// import these:
using System.Net.Mail;
using System.IO;
using System.Text;

// inside your class, create a regular old MailMessage object
MailMessage message = new MailMessage();

// TODO: set the message subject, body, recipients, etc...

string fileContents = "Thanks for the code, Jason!";

// you need a MemoryStream in order to create an attachment w/o saving the file
MemoryStream ms = new MemoryStream(
    ASCIIEncoding.ASCII.GetBytes(fileContents)
);

// now that you have a MemoryStream, attaching it is easy:
message.Attachments.Add(
    new Attachment(ms, "myfile.txt")
    );

// TODO: send the message as you normally would

I’ve only included the code relevant to the attachment because everything else is exactly the same as sending an email normally.

If you wanted to do the same with an image file, for example, you might try something like this:

using System.Drawing.Imaging;

// TODO: all of the Email stuff from the above example

Image img = GetMyImage();  //  assuming GetMyImage returns System.Drawing.Image

MemoryStream ms = new MemoryStream();
img.Save(ms, ImageFormat.Png);

// TODO: the rest of the attachment process is the same as above