sendmail, 4th Edition

Milter xxfi_negotiate()

Redefine one’s abilities at runtime V8.14 and later

Prior to V8.14, a Milter declared its intentions once from main() by calling the smfi_register() routine (Milter smfi_register() on page 1194). The arguments passed to smfi_register() are of type struct smfiDesc and look, in part, like this:

struct smfiDesc
{
    char            *name;
    int             version;
    unsigned long             flags;
    sfsistat             funct;        /* for xxfi_connect */
    sfsistat             funct;        /* for xxfi_helo */
    sfsistat             funct;        /* for xxfi_envfrom */
    sfsistat             funct;        /* for xxfi_envrcpt */
    sfsistat             funct;        /* for xxfi_header */
... etc.

Here, the flags state your intention to perform selected actions, such as to remove recipients, or to replace headers. Each of the funct lines provides a pointer to a function that will handle that phase of the SMTP Milter conversation. If the second funct, for example, were expressed as NULL, the xxfi_ function that handles HELO/EHLO will not be called. But if that second funct were instead a function name, such as the name xxfi_helo() or myDoHelo(), that function will be called to handle the HELO/EHLO phase of the SMTP transaction.

Beginning with V8.14 sendmail, more functions may be called at additional points in the SMTP conversation, and more flags may be set than with earlier sendmail versions. This can lead to problems when a single Milter is connected to by multiple sendmail servers (perhaps across a network of MTAs). One sendmail may be V8.14 and able to recognize the SMFIS_SKIP flag so that the xxfi_body ...