adjust the default configuration to fit Postfix 2.4

postfix/postfix.txt

@@ -107,6 +107,7 @@ smtp      unix  -       -       n       -       -       smtp
 relay     unix  -       -       n       -       -       smtp -o fallback_relay=
 showq     unix  n       -       n       -       -       showq
 error     unix  -       -       n       -       -       error
+retry     unix  -       -       n       -       -       error
 local     unix  -       n       n       -       -       local
 virtual   unix  -       n       n       -       -       virtual
 lmtp      unix  -       -       n       -       -       lmtp