http://www.ckdhr.com/ckd/qmail-103.patch

Description from http://qmail.ruk.cuni.cz/top.html :
Christopher K. Davis has a patch to accept oversize DNS packets which works on
both qmail's dns.c and tcpserver's dns.c. If you don't want to patch qmail, you
can ameliorate the problem somewhat using djbdns, which returns only the
records you ask for, making for a smaller ANSWER section. 

--- qmail-1.03/dns.c.103	Mon Aug 17 16:06:58 1998
+++ qmail-1.03/dns.c	Wed Aug 26 16:28:56 1998
@@ -21,10 +21,12 @@
 static unsigned short getshort(c) unsigned char *c;
 { unsigned short u; u = c[0]; return (u << 8) + c[1]; }
 
-static union { HEADER hdr; unsigned char buf[PACKETSZ]; } response;
+static struct { unsigned char *buf; } response;
+static int responsebuflen = 0;
 static int responselen;
 static unsigned char *responseend;
 static unsigned char *responsepos;
+static unsigned long saveresoptions;
 
 static int numanswers;
 static char name[MAXDNAME];
@@ -45,18 +47,33 @@
  errno = 0;
  if (!stralloc_copy(&glue,domain)) return DNS_MEM;
  if (!stralloc_0(&glue)) return DNS_MEM;
- responselen = lookup(glue.s,C_IN,type,response.buf,sizeof(response));
+ if (!responsebuflen)
+  if (response.buf = (unsigned char *)alloc(PACKETSZ+1))
+   responsebuflen = PACKETSZ+1;
+  else return DNS_MEM;
+
+ responselen = lookup(glue.s,C_IN,type,response.buf,responsebuflen);
+ if ((responselen >= responsebuflen) ||
+     (responselen > 0 && (((HEADER *)response.buf)->tc)))
+  {
+   if (responsebuflen < 65536)
+    if (alloc_re(&response.buf, responsebuflen, 65536))
+     responsebuflen = 65536;
+    else return DNS_MEM;
+    saveresoptions = _res.options;
+    _res.options |= RES_USEVC;
+    responselen = lookup(glue.s,C_IN,type,response.buf,responsebuflen);
+    _res.options = saveresoptions;
+  }
  if (responselen <= 0)
   {
    if (errno == ECONNREFUSED) return DNS_SOFT;
    if (h_errno == TRY_AGAIN) return DNS_SOFT;
    return DNS_HARD;
   }
- if (responselen >= sizeof(response))
-   responselen = sizeof(response);
  responseend = response.buf + responselen;
  responsepos = response.buf + sizeof(HEADER);
- n = ntohs(response.hdr.qdcount);
+ n = ntohs(((HEADER *)response.buf)->qdcount);
  while (n-- > 0)
   {
    i = dn_expand(response.buf,responseend,responsepos,name,MAXDNAME);
@@ -66,7 +83,7 @@
    if (i < QFIXEDSZ) return DNS_SOFT;
    responsepos += QFIXEDSZ;
   }
- numanswers = ntohs(response.hdr.ancount);
+ numanswers = ntohs(((HEADER *)response.buf)->ancount);
  return 0;
 }