diff -rU3 cacert.orig/includes/general.php cacert/includes/general.php
--- cacert.orig/includes/general.php	2007-07-13 19:39:57.000000000 +0200
+++ cacert/includes/general.php	2007-07-17 14:10:33.000000000 +0200
@@ -644,7 +644,7 @@
 						$line = fgets($fp, 4096);
 					if(substr($line, 0, 3) != "250")
 						continue;
-					fputs($fp, "MAIL FROM: <returns@cacert.org>\r\n");
+					fputs($fp, "MAIL FROM: <>\r\n");
 					$line = fgets($fp, 4096);
 
 					if(substr($line, 0, 3) != "250")

diff -rU3 cacert.orig/includes/account.php cacert/includes/account.php
--- cacert.orig/includes/account.php	2007-07-13 19:39:57.000000000 +0200
+++ cacert/includes/account.php	2007-07-17 14:05:42.000000000 +0200
@@ -57,7 +57,11 @@
 		if($checkemail != "OK")
 		{
 			showheader(_("My CAcert.org Account!"));
-			echo "<p>"._("Email Address given was invalid, or a test connection couldn't be made to your server, or the server rejected the email address as invalid")."</p>\n";
+			if (substr($checkemail, 0, 1) == "4") {
+				echo "<p>"._("The mail server responsible for your domain indicated a temporary failure. This may be due to anti-SPAM measures, such as \"greylisting\". Please try again in a few minutes.")."</p>\n";
+			} else {
+				echo "<p>"._("Email Address given was invalid, or a test connection couldn't be made to your server, or the server rejected the email address as invalid")."</p>\n";
+			}
 			echo "<p>$checkemail</p>\n";
 			showfooter();
 			exit;
@@ -475,7 +479,11 @@
 		if($checkemail != "OK")
 		{
 			showheader(_("My CAcert.org Account!"));
-			echo "<p>"._("Email Address given was invalid, or a test connection couldn't be made to your server, or the server rejected the email address as invalid")."</p>\n";
+			if (substr($checkemail, 0, 1) == "4") {
+				echo "<p>"._("The mail server responsible for your domain indicated a temporary failure. This may be due to anti-SPAM measures, such as \"greylisting\". Please try again in a few minutes.")."</p>\n";
+			} else {
+				echo "<p>"._("Email Address given was invalid, or a test connection couldn't be made to your server, or the server rejected the email address as invalid")."</p>\n";
+			}
 			echo "<p>$checkemail</p>\n";
 			showfooter();
 			exit;
diff -rU3 cacert.orig/www/index.php cacert/www/index.php
--- cacert.orig/www/index.php	2007-02-23 22:42:21.000000000 +0100
+++ cacert/www/index.php	2007-07-17 13:54:47.000000000 +0200
@@ -484,7 +484,12 @@
 			if($checkemail != "OK")
 			{
 				$id = 1;
-				$_SESSION['_config']['errmsg'] .= _("Email Address given was invalid, or a test connection couldn't be made to your server, or the server rejected the email address as invalid")."<br>\n$checkemail<br>\n";
+				if (substr($checkemail, 0, 1) == "4") {
+					$_SESSION['_config']['errmsg'] .= _("The mail server responsible for your domain indicated a temporary failure. This may be due to anti-SPAM measures, such as \"greylisting\". Please try again in a few minutes.");
+				} else {
+					$_SESSION['_config']['errmsg'] .= _("Email Address given was invalid, or a test connection couldn't be made to your server, or the server rejected the email address as invalid");
+				}
+				$_SESSION['_config']['errmsg'] .= "<br>\n$checkemail<br>\n";
 			}
 		}