+ 7. The new variables $sender_verify_failure and $recipient_verify_failure
+ contain information about exactly what failed. In an ACL, after one of
+ these failures, the relevant variable contains one of the following words:
+
+ qualify the address was unqualified (no domain), and the message
+ was neither local nor came from an exempted host;
+
+ route routing failed;
+
+ mail routing succeeded, and a callout was attempted; rejection
+ occurred at or before the MAIL command (that is, on initial
+ connection, HELO, or MAIL);
+
+ recipient the RCPT command in a callout was rejected;
+
+ postmaster the postmaster check in a callout was rejected.
+
+ The main use of these variables is expected to be to distinguish between
+ rejections of MAIL and rejections of RCPT.
+
+