<ABOUT EMAIL>
System.Net.Mail - How to add Alternate views and Embed Images
System.Net.Mail provides us with a very intuitive object model to construct
and send an email message.
These days almost all the web and windows email clients gives us more
control over the email content we wish to view (a.k.a HTML view, plain text
view). This is to make us aware that the email content we are viewing may
contain explicit images or externally linked images. Now imagine the
recipient have disabled HTML content in his/her settings then the email
content will be displayed as is(with HTML tags).
We definitely don't want garbled text to be viewed by the recipient, now
here is where the Alternate view comes to our rescue. As the name suggests
it allows us to add alternate content that can be viewed by the receipient
in case HTML content is disabled in his/her settings.
Similarly many web/windows email clients disable external images in the mail
message to avoid linking of external images we can use the LinkedResource to
embed images in our email message.
Although the core topic is about adding alternate views and embedding
resources(images, etc) to an email, I will also touch upon configuration
settings in web.config and Network Credentials.
*MailMessage*:
The MailMessage class plays a key role by wrapping all the email details
like
- From address
- To address (collection)
- CC address (collection)
- BCC address (collection)
- Email Subject
- Email Body
- Priority
- Delivery notification options
- Alternate views (Plain text, HTML)
- Linked Resources (images, etc)
Below given is a typical code used to send an email, the code is pretty
straight forward apart from the AlternateViews, LinkedResources and some
SMTPClient config section.
//========================================================
MailMessage objMailMessage = new MailMessage();
//File Attachment
if (fileUploadEmailAttachment.HasFile)
{
objMailMessage.Attachments.Add(
new Attachment(
fileUploadEmailAttachment.FileContent,
fileUploadEmailAttachment.FileName));
}
//From
objMailMessage.From = new MailAddress(txtEmailFrom.Text,
txtDisplayName.Text);
//To
objMailMessage.To.Add(new MailAddress(txtEmailTo.Text));
//CC
if (txtEmailCC.Text.Length > 0)
{
objMailMessage.CC.Add(new MailAddress(txtEmailCC.Text));
}
//BCC
if (txtEmailBCC.Text.Length > 0)
{
objMailMessage.Bcc.Add(new MailAddress(txtEmailBCC.Text));
}
//Subject
objMailMessage.Subject = txtSubject.Text;
//Plain Text Alternative Email Content
AlternateView objPlainAltView = AlternateView.CreateAlternateViewFromString(
txtAlternateView.Text);
objMailMessage.AlternateViews.Add(objPlainAltView);
//HTML Alternative Email Content
LinkedResource objLinkedRes = new LinkedResource(
Server.MapPath(".")
+ "\\fuzzydev-logo.jpg", "image/jpeg");
objLinkedRes.ContentId = "fuzzydev-logo";
AlternateView objHTLMAltView = AlternateView.CreateAlternateViewFromString(
txtHTMLBody.Text,
new System.Net.Mime.ContentType("text/html"));
objHTLMAltView.LinkedResources.Add(objLinkedRes);
objMailMessage.AlternateViews.Add(objHTLMAltView);
//High Priority
objMailMessage.Priority = MailPriority.High;
//Notify On Sucessfull Delivery
objMailMessage.DeliveryNotificationOptions =
DeliveryNotificationOptions.OnSuccess;
SmtpClient objSMTPClient = new SmtpClient(txtHostName.Text);
objSMTPClient.DeliveryMethod = SmtpDeliveryMethod.Network;
if(chkBoxEnableSSL.Checked)
objSMTPClient.EnableSsl = true;
//Credentials (username, password)
string sUserName = txtEmailFrom.Text.Split('@')[0];
objSMTPClient.Credentials = new System.Net.NetworkCredential(
sUserName, txtEmailFromPassword.Text);
//Send Email
objSMTPClient.Send(objMailMessage);
//========================================================
Now let me concentrate on the Alternateview, adding an alternate view is
very easy, just create an object of the AlternateView class using the static
method of the *AlternateView* class called
*CreateAlternateViewFromString*passing the email text and the MIME
type.
*For example if we want to create a plain text view then we will do
something like this*
AlternateView objPlainAltView = AlternateView .CreateAlternateViewFromString(
txtAlternateView.Text);
objMailMessage.AlternateViews.Add(objPlainAltView);
*Now if we need HTML view then*
AlternateView objHTLMAltView = AlternateView.CreateAlternateViewFromString(
txtHTMLBody.Text,
new System.Net.Mime.ContentType("text/html"));
objMailMessage.AlternateViews.Add(objHTLMAltView);
That looks pretty simple, now the good news is the recipient will view the
email message based on the email clients settings. So if HTML content is
disabled then plain text message is displayed otherwise the HTML content is
displayed.
Let us move forward and get our hands dirty by embedding an image in an HTML
content message. In order to embed an image in our email we can use
LinkedResource class, we can add this object to the LinkedResource
collection of the AlternateView object.
LinkedResource objLinkedRes = new LinkedResource(
Server.MapPath(".")
+ "\\fuzzydev-logo.jpg",
"image/jpeg");
objLinkedRes.ContentId = "fuzzydev-logo";
AlternateView objHTLMAltView = AlternateView.CreateAlternateViewFromString(
"
![]()
",
new System.Net.Mime.ContentType("text/html"));
objHTLMAltView.LinkedResources.Add(objLinkedRes);
objMailMessage.AlternateViews.Add(objHTLMAltView);
In the above code we are passing an image file path and also specifying the
content type as an jpeg image to the LinkedResource object. Next line of
code is very interesting, we are assigning a unique ContentId which will be
used to set the src of our HTML image tag. In our case the content id is
fuzzydev-logo and if you look at the HTML alternate view object in the
constructor section we are having an image tag which refers to the same
content id.
Now it's the email clients responsibility to understand the embedded
resource and the reference in the image tag and display the image.
*SMTPClient:*
Now coming to the SMTP client configuration, let's just look in to what is
the minimum configuration settings that SMTP client object expects from us.
- Host name or IP address
- Delivery Method (Network, Pick up directory from IIS, custom pickup
directory)
- EnableSsl (whether Secured Socket Layer is required)
- Credentials (user name, password)
*SMTPClient configuration in web.config:*
<configuration>
<system.net>
<mailsettings>
<smtp deliverymethod="Network" from="from@domain.com">
<network host="smtp.gmail.com">
userName="email user name"
password="email passowrd"
/>
<system.web>
<compilation debug="false">
<pages validaterequest="false">
The above configuration helps us in quickly changing the delivery method,
from mail address, host name (or IP address) , user name and password.
Although the configuration is not mandatory it is the recommended way of
implementing the email functionality.
Below given code doesn't depend on the web.config for it's configuration
needs
SmtpClient objSMTPClient = new SmtpClient(txtHostName.Text);
objSMTPClient.DeliveryMethod = SmtpDeliveryMethod.Network;
if(chkBoxEnableSSL.Checked)
objSMTPClient.EnableSsl = true;
//Credentials (username, password)
string sUserName = txtEmailFrom.Text.Split('@')[0];
objSMTPClient.Credentials = new System.Net.NetworkCredential(
sUserName, txtEmailFromPassword.Text);
//Send Email
objSMTPClient.Send(objMailMessage);
We don't need to specify the host name, etc if it's available in the
web.config, this is usefull as in different part's of our application we can
just use the specified configuration and if required then specify manually.
Now that deserves a round applause for those involved in the development of
System.Net.Mail classes.
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