Xojo Plugin

Add a Custom Header to a Related Item

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Demonstrates the Chilkat Email.AddRelatedHeader method, which adds a custom MIME header field to an existing related item identified by its zero-based index. This example first adds a related style sheet (which becomes index 0) and captures its generated Content-ID, builds an HTML body that references the style sheet by that cid:, then attaches an extra header field to the related item and prints the resulting MIME.

Background: Like attachments, each related item (an inline image, style sheet, etc.) is a MIME part with its own small header block describing that part — Content-Type, Content-ID, Content-Location, and so on. AddRelatedHeader lets you insert additional fields into that per-part block, which is occasionally required for interoperability with clients that look for specific custom headers on embedded resources.

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//  Demonstrates the AddRelatedHeader method, which adds a custom MIME header field to an
//  existing related item, identified by its zero-based index.

Dim email As New Chilkat.Email
email.Subject = "Related item with a custom header"

//  Add a related item first (a style sheet); capture its generated Content-ID.  It becomes
//  related-item index 0.
Dim cid As String
cid = email.AddRelatedString("styles.css","body { color: black; }","utf-8")
If (email.LastMethodSuccess = False) Then
    System.DebugLog(email.LastErrorText)
    Return
End If

//  Build the HTML body, referencing the related style sheet by its Content-ID.  A
//  placeholder is used and then replaced with the actual Content-ID.
Dim sbHtml As New Chilkat.StringBuilder
Dim success As Boolean
success = sbHtml.Append("<html><head><link rel=""stylesheet"" href=""cid:PLACEHOLDER_CID""/></head><body>Styled content.</body></html>")
Dim numReplaced As Int32
numReplaced = sbHtml.Replace("PLACEHOLDER_CID",cid)
email.SetHtmlBody sbHtml.GetAsString()

//  Add a custom header field to the first related item (index 0).
email.AddRelatedHeader 0,"X-Custom-Related-Header","some value"

//  The custom header now appears in the related item's MIME part.
System.DebugLog(email.GetMime())