https://bugs.cacert.org/view.php?id=436

includes/account.php

@@ -57,7 +57,12 @@
 		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>$checkemail</p>\n";
 			showfooter();
 			exit;
@@ -475,7 +480,13 @@
 		if($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";
+			//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;