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Add a Custom Header to a Related Item

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.

loEmail = createobject("CkEmail")
loEmail.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.
lcCid = loEmail.AddRelatedString("styles.css","body { color: black; }","utf-8")
if (loEmail.LastMethodSuccess = .F.) then
    ? loEmail.LastErrorText
    release loEmail
    return
endif

//  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.
loSbHtml = createobject("CkStringBuilder")
loSbHtml.Append('<html><head><link rel="stylesheet" href="cid:PLACEHOLDER_CID"/></head><body>Styled content.</body></html>')
lnNumReplaced = loSbHtml.Replace("PLACEHOLDER_CID",lcCid)
loEmail.SetHtmlBody(loSbHtml.GetAsString())

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

//  The custom header now appears in the related item's MIME part.
? loEmail.GetMime()


release loEmail
release loSbHtml