Only run validatesender if the client is untrusted.
This means that validatesender will get run once when
the message arrives from outside but not as relayed
internally and run through spam checking.
Previously we were running validatesender twice for
each incoming message, and the second one was redundant.

Reference: /n/sources/patch/applied/smtpd-trust-inside-sender
Date: Mon May 22 02:02:29 CES 2006
Signed-off-by: geoff@collyer.net

--- /sys/src/cmd/upas/smtp/smtpd.c	Mon May 22 02:00:07 2006
+++ /sys/src/cmd/upas/smtp/smtpd.c	Mon May 22 02:00:01 2006
@@ -1152,7 +1152,7 @@
 		rejectcount++;
 		return;
 	}
-	if(sendermxcheck()){
+	if(!trusted && sendermxcheck()){
 		rerrstr(errx, sizeof errx);
 		if(strncmp(errx, "rejected:", 9) == 0)
 			reply("554 %s\r\n", errx);