Backported from 2.3:

	Bugfix: the SMTP server now separates the message size check
	from the queue space check, so that the size check can be
	done before an SMTPD proxy filter. Files: smtpd/smtpd.c,
	smtpd/smtpd_check.c.

diff -ur postfix-2.2.3/src/smtpd/smtpd.c postfix-2.2.3-size/src/smtpd/smtpd.c
--- postfix-2.2.3/src/smtpd/smtpd.c	2005-03-09 21:07:43.000000000 +0100
+++ postfix-2.2.3-size/src/smtpd/smtpd.c	2005-09-07 01:57:23.933600904 +0200
@@ -1555,6 +1555,10 @@
 	    return (-1);
 	}
     }
+    if ((err = smtpd_check_size(state, state->msg_size)) != 0) {
+	smtpd_chat_reply(state, "%s", err);
+	return (-1);
+    }
     if (verp_delims && argv[2].strval[0] == 0) {
 	smtpd_chat_reply(state, "503 Error: %s requires non-null sender",
 			 VERP_CMD);
@@ -1573,7 +1577,7 @@
      * Check the queue file space, if applicable.
      */
     if (!USE_SMTPD_PROXY(state)) {
-	if ((err = smtpd_check_size(state, state->msg_size)) != 0) {
+	if ((err = smtpd_check_queue(state)) != 0) {
 	    smtpd_chat_reply(state, "%s", err);
 	    return (-1);
 	}
diff -ur postfix-2.2.3/src/smtpd/smtpd_check.c postfix-2.2.3-size/src/smtpd/smtpd_check.c
--- postfix-2.2.3/src/smtpd/smtpd_check.c	2005-03-05 02:13:10.000000000 +0100
+++ postfix-2.2.3-size/src/smtpd/smtpd_check.c	2005-09-07 02:04:32.193697648 +0200
@@ -39,6 +39,13 @@
 /*
 /*	char	*smtpd_check_eod(state)
 /*	SMTPD_STATE *state;
+/*
+/*	char	*smtpd_check_size(state, size)
+/*	SMTPD_STATE *state;
+/*	off_t	size;
+/*
+/*	char	*smtpd_check_queue(state)
+/*	SMTPD_STATE *state;
 /* DESCRIPTION
 /*	This module implements additional checks on SMTP client requests.
 /*	A client request is validated in the context of the session state.
@@ -101,11 +108,13 @@
 /* .PP
 /*	smtpd_check_size() checks if a message with the given size can
 /*	be received (zero means that the message size is unknown).  The
-/*	message is rejected when:
-/* .IP \(bu
-/*	The message size exceeds the non-zero bound specified with the
+/*	message is rejected when
+/*	the message size exceeds the non-zero bound specified with the
 /*	\fImessage_size_limit\fR configuration parameter. This is a
 /*	permanent error.
+/*
+/*	smtpd_check_queue() checks the available queue file system
+/*	space.  The message is rejected when:
 /* .IP \(bu
 /*	The available queue file system space is less than the amount
 /*	specified with the \fImin_queue_free\fR configuration parameter.
@@ -4115,8 +4124,6 @@
 
 char   *smtpd_check_size(SMTPD_STATE *state, off_t size)
 {
-    char   *myname = "smtpd_check_size";
-    struct fsspace fsbuf;
     int     status;
 
     /*
@@ -4127,16 +4134,38 @@
 	return (status == SMTPD_CHECK_REJECT ? STR(error_text) : 0);
 
     /*
-     * Avoid overflow/underflow when comparing message size against available
-     * space.
+     * Check against file size limit.
      */
-#define BLOCKS(x)	((x) / fsbuf.block_size)
 
     if (var_message_limit > 0 && size > var_message_limit) {
 	(void) smtpd_check_reject(state, MAIL_ERROR_POLICY,
 				  "552 Message size exceeds fixed limit");
 	return (STR(error_text));
     }
+    return (0);
+}
+
+/* smtpd_check_queue - check queue space */
+
+char   *smtpd_check_queue(SMTPD_STATE *state)
+{
+    char   *myname = "smtpd_check_queue";
+    struct fsspace fsbuf;
+    int     status;
+
+    /*
+     * Return here in case of serious trouble.
+     */
+    SMTPD_CHECK_RESET();
+    if ((status = setjmp(smtpd_check_buf)) != 0)
+	return (status == SMTPD_CHECK_REJECT ? STR(error_text) : 0);
+
+    /*
+     * Avoid overflow/underflow when comparing message size against available
+     * space.
+     */
+#define BLOCKS(x)	((x) / fsbuf.block_size)
+
     fsspace(".", &fsbuf);
     if (msg_verbose)
 	msg_info("%s: blocks %lu avail %lu min_free %lu msg_size_limit %lu",
diff -ur postfix-2.2.3/src/smtpd/smtpd_check.h postfix-2.2.3-size/src/smtpd/smtpd_check.h
--- postfix-2.2.3/src/smtpd/smtpd_check.h	2004-11-19 14:23:23.000000000 +0100
+++ postfix-2.2.3-size/src/smtpd/smtpd_check.h	2005-09-07 02:02:10.668212792 +0200
@@ -19,6 +19,7 @@
 extern char *smtpd_check_helo(SMTPD_STATE *, char *);
 extern char *smtpd_check_mail(SMTPD_STATE *, char *);
 extern char *smtpd_check_size(SMTPD_STATE *, off_t);
+extern char *smtpd_check_queue(SMTPD_STATE *);
 extern char *smtpd_check_rcpt(SMTPD_STATE *, char *);
 extern char *smtpd_check_etrn(SMTPD_STATE *, char *);
 extern char *smtpd_check_data(SMTPD_STATE *);