sendmail, 4th Edition

Milter xxfi_helo()

Process a HELO/EHLO command All Milter versions

After the client connects to the listening sendmail server, and after sendmail has sent its 220 greeting, the client will usually send a HELO or EHLO command to greet sendmail and to declare its use of ESMTP extensions:

220 your.host.domain ESMTP Sendmail 8.14.1/8.14.1; Fri, 12 Dec 2007 06:06:10 −0800
(PST)
HELO client name here                        ← do not use ESMTP extensions
EHLO client name here                        ← use ESMTP extensions

After the client has sent its HELO or EHLO greeting, and before sendmail replies to that greeting, your xxfi_helo() function, if used, is called.

The xxfi_helo() function is called like this:

sfsistat
xxfi_helo(SMFICTX *ctx, char *helohost)

Here, ctx is the context pointer passed to all xxfi_ functions to maintain state in a multithreaded environment. The helohost is the client’s hostname as supplied along with the HELO or EHLO greeting. It is a zero-terminated string that contains the literal text supplied by the client to the HELO or EHLO greeting. That text should be a canonical hostname, but may turn out to be almost anything, so your xxfi_helo() function should practice defensive programming:

""
"foo"
"bob.is.a.happy.boy"

The HELO or EHLO command is optional. The connecting client may elect to omit sending this command and instead skip ahead and send the MAIL From: command. Thus, your xxfi_helo() may not be called for any given connection. If you wish to ensure that it is called, set one of the following in your mc configuration ...