[2024-03-14 12:46] Omar Polo <op@omarpolo.com>
>
> [...]
>
> (also a bit unsure about the exact wording, but since we don't have any
> documentation on MDAs, better get this in the tree first and then
> bikeshed later about it :-)

I'm also unsure about the exact wording and some aspect are not that
clear. But I would also say this version is better then nothing.

Here is a patch with including your feedback. 

Philipp

diff --git a/usr.sbin/smtpd/mda_unpriv.c b/usr.sbin/smtpd/mda_unpriv.c
index 1d59550aead..d2e67f66164 100644
--- a/usr.sbin/smtpd/mda_unpriv.c
+++ b/usr.sbin/smtpd/mda_unpriv.c
@@ -28,7 +28,7 @@ mda_unpriv(struct dispatcher *dsp, struct deliver *deliver,
     const char *pw_name, const char *pw_dir)
 {
 	int		idx;
-	char	       *mda_environ[11];
+	char	       *mda_environ[12];
 	char		mda_exec[LINE_MAX];
 	char		mda_wrapper[LINE_MAX];
 	const char     *mda_command;
@@ -54,6 +54,7 @@ mda_unpriv(struct dispatcher *dsp, struct deliver *deliver,
 	xasprintf(&mda_environ[idx++], "PATH=%s", _PATH_DEFPATH);
 	xasprintf(&mda_environ[idx++], "DOMAIN=%s", deliver->rcpt.domain);
 	xasprintf(&mda_environ[idx++], "HOME=%s", pw_dir);
+	xasprintf(&mda_environ[idx++], "ORIGINAL_RECIPIENT=%s@%s", deliver->rcpt.user, deliver->rcpt.domain);
 	xasprintf(&mda_environ[idx++], "RECIPIENT=%s@%s", deliver->dest.user, deliver->dest.domain);
 	xasprintf(&mda_environ[idx++], "SHELL=/bin/sh");
 	xasprintf(&mda_environ[idx++], "LOCAL=%s", deliver->rcpt.user);
diff --git a/usr.sbin/smtpd/smtpd.conf.5 b/usr.sbin/smtpd/smtpd.conf.5
index 257ad172dc4..c668d15d0dc 100644
--- a/usr.sbin/smtpd/smtpd.conf.5
+++ b/usr.sbin/smtpd/smtpd.conf.5
@@ -1113,6 +1113,34 @@ For example, with recipient
 .It %{rcpt}     Ta expands to Dq user+t:g@example.org
 .It %{rcpt:raw} Ta expands to Dq user+t?g@example.org
 .El
+.Ss MDA ENVIRONMENT
+When a MDA is invoked,
+.Xr smtpd 8
+will create a new process.
+Only the uid and gid of the destination user is set.
+The following environment variables will be set:
+.Bl -tag -width "ORIGINAL_RECIPIENT"
+.It Ev DOMAIN
+The recipient domain.
+.It Ev HOME
+The home directory of the destination user.
+.It Ev RECIPIENT
+The address of the final recipient.
+.It Ev ORIGINAL_RECIPIENT
+The address of the original recipient.
+.It Ev EXTENSION
+The sub address of the recipient, only set when there is a sub address.
+.It Ev SENDER
+The address of the sender (might be empty).
+.El
+.Pp
+This process gets the mail piped to
+.Xr stdin 3 .
+A mail is considered as delivered when the mda exit with
+.Dv EX_OK
+and
+.Xr stdin 3
+is completely read.
 .Sh FILES
 .Bl -tag -width "/etc/mail/smtpd.confXXX" -compact
 .It Pa /etc/mail/smtpd.conf