sendmail, 4th Edition

Milter smfi_addheader()

Conditionally insert a header All sendmail versions

To add a header to the existing headers in a message you may use either this smfi_addheader() routine or the smfi_insheader() routine (Milter smfi_insheader() on page 1192). This routine is conditional in that it will replace some headers and insert others, whereas the smfi_insheader() routine is unconditional and always inserts headers. With this smfi_addheader() special logic inside sendmail scans headers to see whether the new header name already exists. If that header name exists, and if that header is not a trace header (such as Received:), and if that header is not an X- header nor one added by another Milter, sendmail will silently replace the existing named header’s value with the new value, rather than adding the new header.^[448]

Before you may add headers, you must first declare your intention to do so by including the SMFIF_ADDHDRS flag to the flags portion of the smfiDesc structure:

struct smfiDesc smfilter =
{
    ...
    SMFIF_ADDHDRS,/* flags */
    ...

Failure to include this flag causes smfi_addheader() to return MI_FAILURE every time it is called.

You add headers to a message by calling this smfi_addheader() routine from inside your xxfi_eom() function (Milter xxfi_eom() on page 1215):

ret = smfi_addheader(ctx, name, value);

The first argument is the usual ctx connection-context pointer. It is the same ctx pointer that was passed to the enclosing xxfi_eom() function. It may not be NULL and must be a valid ...