Interop.Outlook Message in HTML displayed as Plain Text

Question

I recently switched from using EWS to using Interop.Outlook (see this article). The process is extremely easy to use!

Unfortunately, I have one problem that did not exist in EWS: Outlook does not process the HTML body even when BodyFormat is set to true. In this code sample (VB.NET), the MessageBody does start with < HTML. With debug, I verified that BodyFormat was set to HTML when display was executed. Nevertheless, the email body is displayed as plain text.

Dim Outlook As New Outlook.Application
Dim mail As Outlook.MailItem =  DirectCast(Outlook.CreateItem(Microsoft.Office.Interop.Outlook.OlItemType.olMailItem), Outlook.MailItem)

With mail
    .To = Addr
    .Subject = Subject
    .Body = MessageBody
    .BodyFormat = If(MessageBody.ToLower.StartsWith("<html"),
        Microsoft.Office.Interop.Outlook.OlBodyFormat.olFormatHTML,
        Microsoft.Office.Interop.Outlook.OlBodyFormat.olFormatPlain)
    .Display(Modal)

The exact same body text, when using EWS displays correctly.

Answer 1

  .Body = MessageBody

The Body property of the MailItem class is a string representing the clear-text body of the Outlook item (without formatting). You need to set the body format first (if required). By default Outlook uses the HTML format.

With mail
.To = Addr
.Subject = Subject
If(MessageBody.ToLower.StartsWith("<html")) Then
  .BodyFormat = Microsoft.Office.Interop.Outlook.OlBodyFormat.olFormatHTML
  .HTMLBody = MessageBody
Else
  .BodyFormat = Microsoft.Office.Interop.Outlook.OlBodyFormat.olFormatPlain
  .Body = MessageBody
End If
.Display(Modal)

Use the HTMLBody property for setting an HTML markup.

Or just simply:

 With mail
.To = Addr
.Subject = Subject
If(MessageBody.ToLower.StartsWith("<html")) Then      
  .HTMLBody = MessageBody
Else
  .Body = MessageBody
End If
.Display(Modal)