Introduction
This article presents a complete example of embedding an image in an email message. There are plenty of examples in the Internet; however, they are incomplete.
I spent many hours researching and getting the pieces together, and decided to share the results with my fellow developers.
Background
The code is based on functionality delivered by the .NET Framework (v 2.0, 3.0, and 3.5) which is not very efficient. If you plan to do some heavy emailing, please do not use this code.
The code is in VB, and the example is a one page website using VS 2008. You can copy and paste the code if you are using a previous version of VS.
Using the code
The code is very simple, and can be lifted and incorporated into an application easily. In fact, the basis of the code was used for a project for a client where the recipient's email address is selected from a GridView. (Can't post that one, is work-for-hire!)
Don't forget to update your web.config file! You can add the host and credentials inside the code, but I prefer to use the configuration file. Simply add the following lines to your web.config file:
<system.net>
<mailSettings>
<smtp from="user@somehost.com">
<network host="smtp.somehost.com" password="somepassword"
userName="user@somehost.com" port="587" />
</smtp>
</mailSettings>
</system.net>
The port should be 25, but some ISPs prefer that 587 is used. It makes no difference to the application.
Points of interest
With many of the other examples, you get an email with the graphic attached as a .dat file, not at all what is intended.
The missing ingredient is specifying the type of the attachment and its encoding:
Dim imageResourceEs As New _
System.Net.Mail.LinkedResource(fileImage.PostedFile.FileName, "image/gif")
imageResourceEs.TransferEncoding = Net.Mime.TransferEncoding.Base64
In most other examples, the second parameter is missing when creating the LinkedResource, and they fail to set an encoding for the file; thus it is attached instead of embedded.
Make sure to change the MIME type (image/GIF, image/JPEG, etc.) to match the type of the file you are embedding. The message body is a string formatted with HTML tags. Some renderers will let you do some things while other will balk, your mileage may vary.
The string is the parameter passed to CreateAlternateViewFromString, and as you can see in the example, I use a style to set the font family and size.
htmlView = System.Net.Mail.AlternateView.CreateAlternateViewFromString("<html><body " & _
"style='font-family:Segoe UI, Arial; font-size: 11pt;'><p>" & _
txtBody.Text.Trim & "</p>'<img src='cid:image1'></body></html>", Nothing, "text/html")
Basically, what we're doing is creating an "anchor" inside the HTML message with the code img src:'cid imageName' and then defining the resource and linking it so that the HTML renderer can find it.
Another important point is to make sure the name in the img tag in the HTML string is enclosed in quotes (single or double) and that it matches precisely the name of the resource:
img src="cid:image1"
imageResourceEs.ContentId = "image1"
Once you understand that we are using the img tag to allocate the "space" inside the HTML message and linking the resource so it can be found, you will see that adding multiple images is a matter of creating multiple tags and linking multiple resources:
!Inside the HTML message create the "holders" for the images
img src="cid:image1"
img src="cid:image2"
! Create the resources
Dim lkImage1 As New
System.Net.Mail.LinkedResource(FileName, "image/gif")
Dim lkImage2 As New
System.Net.Mail.LinkedResource(FileName, "image/gif")
! Link the resources
lkImage1.ContentId = "image1"
lkImage2.ContentId = "image2"
The message is displayed correctly in Gmail:
and Outlook:
I have tested the code with other email engines such as Yahoo! and others, but not Hotmail. It should work, but Hotmail is very quirky when rendering HTML messages.
The code also creates a "text view" incorporating the "body" of the message without the graphic element, so that something is displayed if the email client can't display the HTML version.
Enjoy!
History
- First version: December 19, 2008.
