Mailkit Displaying Inline logo As Attachment-CodePudding

I am using Mailkit with an aspx email template with an image control for the logo. The email sends ok, but the inline logo is being sent as an attachment. I have spent days looking at similar issues and examples here but cant figure out what the problem is in my own case. I need the image to show in the body of the message and Not as attachment.

Here is the code file:

Private Sub EmailCustomer()


    Dim ToAddress As String = CustomerEmail
    Const FromAddress As String = "[email protected]"

    Try

        Dim mail As MimeMessage
        Dim bodybuilder As New BodyBuilder
        mail = New MimeMessage()
        mail.From.Add(New MailboxAddress("", FromAddress.ToUpper))
        mail.To.Add(New MailboxAddress("", CustomerEmail))
        mail.Subject = "Order Confirmation"

        Dim contentType As New ContentType("image", "png")
        Dim contentId = MimeUtils.GenerateMessageId()
        Dim image = CType(bodybuilder.LinkedResources.Add(Server.MapPath(".") & "/Img/MainLogo.png", contentType), MimePart)
        image.ContentTransferEncoding = ContentEncoding.Default
        image.ContentId = contentId

        image.ContentDisposition = New ContentDisposition() With {.Disposition = ContentDisposition.Inline}

        bodybuilder.HtmlBody = PopulateEmailHtmlBody(CustomerEmail, Session("GatewayOrderID"), "cid:" & image.ContentId)



        mail.Body = bodybuilder.ToMessageBody()

        Using client As New MailKit.Net.Smtp.SmtpClient
            client.Connect("xxx", 465, True)
            client.Authenticate(FromAddress, ConfigurationManager.AppSettings("WebMailPsw")) 

            client.AuthenticationMechanisms.Remove("XOAUTH2") 

            client.Send(mail)
            client.Disconnect(True)
        End Using

    Catch ex As Exception
        ShowMessage("Connection issues sending email.", MessageType.Info)
       
    End Try

End Sub

Private Function PopulateEmailHtmlBody(ByVal customeremail As String, ByVal orderid As String, ByVal logoUrl As String) As String
    Using reader As StreamReader = New StreamReader(Server.MapPath("~/OrderStatusEmailTemplate.aspx"))


        Dim body As String = String.Empty
        body = reader.ReadToEnd
        body = body.Replace("{LogoUrl}", logoUrl)
        body = body.Replace("{CustomerEmail}", customeremail)

        body = body.Replace("{OrderID}", orderid)
        Return body

    End Using
End Function

Here is the template:

<body>
    <form id="form1" runat="server">
        <asp:ScriptManager ID="Scriptmanager1" runat="server" ></asp:ScriptManager>
        
         

        <div class="row">
            <div style="background: #40B800; width: 100%; height: 10px;">
            </div>
        </div>

        <div id="logoDiv" style="border-bottom: solid 4px #919191; padding-bottom: 2px">

           <asp:Image ID="logo" runat="server" src="{logourl}"/>
        </div>


        <br />
        Hello <em>{CustomerEmail} </em>
        <br />
        <br />
        
       Your Order was placed successfully with OrderID:
 <em>{OrderID} </em> 
       This Order has been forwarded  for payment processing.  Your Order shall be processed and shipped when this process completes.
         <br />
        <br />
       Yours faithfully
         
        <br />
       For: Xxx.
       

         <div class="row">
            <div style="background-color: #eaeaea; border-top:    solid 2px #919191">
            </div>
        </div>
    </form>
</body>

Here is part of the raw data:

Message-Id: <SHDL2FYG7FU4.BD3A7K1JDSQJ@plesk3001>
To:xxxx
MIME-Version: 1.0
Content-Type: multipart/related;
boundary="=-    4ZC71hL1CWyK9Sdx8oPqnQ=="; type="text/html"

--=-4ZC71hL1CWyK9Sdx8oPqnQ==
Content-Type: text/html; charset=utf-8
Content-Id: <TPQO2FYG7FU4.UIEK2B0GWEC33@plesk3001>

And here:

--=-4ZC71hL1CWyK9Sdx8oPqnQ==
Content-Type: image/png; name=MainLogo.png
Content-Transfer-Encoding: base64
Content-Location: MainLogo.png
Content-Id: <SHDL2FYG7FU4.7PB5WR21L9MX@plesk3001>
Content-Disposition: inline


 --=-4ZC71hL1CWyK9Sdx8oPqnQ==--

And here is how it sends :

Inline logo

CodePudding user response：

Based on the documentation, I don't think you need to set the ContentTransferEncoding or ContentDisposition; you should just need to use:

Dim image As MimeEntity = bodybuilder.LinkedResources.Add(Server.MapPath(".") & "/Img/MainLogo.png", contentType)
image.ContentId = MimeUtils.GenerateMessageId()

bodybuilder.HtmlBody = PopulateEmailHtmlBody(CustomerEmail, Session("GatewayOrderID"), "cid:" & image.ContentId)

You also don't want to use any server controls in the template, since you're reading the content of the file rather than executing the template.

<body>
    <div class="row">
        <div style="background: #40B800; width: 100%; height: 10px;">
        </div>
    </div>

    <div id="logoDiv" style="border-bottom: solid 4px #919191; padding-bottom: 2px">
        <img src="{logourl}"/>
    </div>

    <br />
    Hello <em>{CustomerEmail} </em>
    <br />
    <br />
        
   Your Order was placed successfully with OrderID: <em>{OrderID} </em> 
   This Order has been forwarded  for payment processing.  Your Order shall be processed and shipped when this process completes.
    <br />
    <br />
    Yours faithfully
         
    <br />
    For: Xxx.
       

    <div class="row">
        <div style="background-color: #eaeaea; border-top: solid 2px #919191">
        </div>
    </div>
</body>

I suspect this second point is the cause of the problem; your email body contains the literal text <asp:Image .../> instead of an <img /> tag, and the email client doesn't know what to do with it.