Apr
15

.NET MailMessage, LinkedResources, AlternateViews and Exceptions

It doesn’t take much to hack together email functionality using the .NET framework.  In most cases you can new-up a MailMessage reference, assign sender and recipient addresses, provide a subject and a message body, configure your SMTP settings and then send.  Done and done.

But let’s say you need to provide both plain text and HTML versions of your message body.  Or maybe you would like to embed an image or two within the message body.  Or, what if, for some reason, you actually want to handle exceptions appropriately.  Well, there’s more to it then.

There are a numerous ways to better organize the following code.  In fact, we just went through an exercise at work where we refactored the heck out of the core email functionality and produce a really clean usable component which can be easily mocked, configured and leverages email templates.  It’s pretty cool.  That being said, I believe the following sample demonstrates the aforementioned core features of .NET emailing. 

I hope it helps. Let me know if I missed anything or it the example could be more clear.

try
{
    // Assign a sender, recipient and subject to new mail message
    MailAddress sender =
        new MailAddress("sender@johnnycoder.com", "Sender");

    MailAddress recipient =
        new MailAddress("recipient@johnnycoder.com", "Recipient");

    MailMessage m = new MailMessage(sender, recipient);
    m.Subject = "Test Message";

    // Define the plain text alternate view and add to message
    string plainTextBody =
        "You must use an email client that supports HTML messages";

    AlternateView plainTextView =
        AlternateView.CreateAlternateViewFromString(
            plainTextBody, null, MediaTypeNames.Text.Plain);

    m.AlternateViews.Add(plainTextView);

    // Define the html alternate view with embedded image and
    // add to message. To reference images attached as linked
    // resources from your HTML message body, use "cid:contentID"
    // in the <img> tag...
    string htmlBody =
        "<html><body><h1>Picture</h1><br>" +
        "<img src=\"cid:SampleImage\"></body></html>";

    AlternateView htmlView =
        AlternateView.CreateAlternateViewFromString(
            htmlBody, null, MediaTypeNames.Text.Html);

    // ...and then define the actual LinkedResource matching the
    // ContentID property as found in the image tag. In this case,
    // the HTML message includes the tag
    // <img src=\"cid:SampleImage\"> and the following
    // LinkedResource.ContentId is set to "SampleImage"
    LinkedResource sampleImage =
        new LinkedResource("sample.jpg",
            MediaTypeNames.Image.Jpeg);
    sampleImage.ContentId = "SampleImage";

    htmlView.LinkedResources.Add(sampleImage);

    m.AlternateViews.Add(htmlView);

    // Finally, configure smtp or alternatively use the
    // system.net mailSettings
    SmtpClient smtp = new SmtpClient
          {
              Host = "smtp.bigcompany.com",
              UseDefaultCredentials = false,
              Credentials =
                  new NetworkCredential("username", "password")
          };

    //<system.net>
    //    <mailSettings>
    //        <smtp deliveryMethod="Network">
    //            <network host="smtp.bigcompany.com"
    //              port="25" defaultCredentials="true"/>
    //        </smtp>
    //    </mailSettings>
    //</system.net>

    smtp.Send(m);
}
catch (ArgumentException)
{
    throw new
        ArgumentException("Undefined sender and/or recipient.");
}
catch (FormatException)
{
    throw new
        FormatException("Invalid sender and/or recipient.");
}
catch (InvalidOperationException)
{
    throw new
        InvalidOperationException("Undefined SMTP server.");
}
catch (SmtpFailedRecipientException)
{
    throw new SmtpFailedRecipientException(
        "The mail server says that there is no mailbox for recipient");
}
catch (SmtpException ex)
{
    // Invalid hostnames result in a WebException InnerException that
    // provides a more descriptive error, so get the base exception
    Exception inner = ex.GetBaseException();
    throw new SmtpException("Could not send message: " + inner.Message);
}

Posted by Ben Griswold ASP.NET, C#, Code Library, Samples Subscribe to RSS feed

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