Experienceing for some domains (i.e. comcast.net)
  CNAME lookup failed temporarily. (#4.4.3)
  I'm not going to try again; this message has been in the queue too long.

Due to DNS response packets larger than 512 bytes cause infinite CNAME lookup failed temporarily and mail loss.

RFC 2821 author advocated simply turning the feature off.
Qmail author advocated simply turning the feature off.

sign-off by John Stile <john@stilen.com>

diff -ruNp a/dns.c b/dns.c
--- a/dns.c    2013-01-30 14:00:37.000000000 -0800
+++ b/dns.c    2013-01-30 14:06:12.000000000 -0800
@@ -187,6 +187,7 @@ int flagsearch;
 int dns_cname(sa)
 stralloc *sa;
 {
+ return 0; /* https://bugs.gentoo.org/show_bug.cgi?id=323517  */
  int r;
  int loop;
  for (loop = 0;loop < 10;++loop)