Yahoo mail (qmail) pukes my DNS information

[D. J. Bernstein]

A very easy way to track down resolution problems is to use dnstrace.
See http://cr.yp.to/djbdns/tools.html#dnstrace.

Brad Knowles writes:
> Dan apparently believes that TCP should never be used for DNS 
> queries, which is why djbdns does not support the use of TCP by 
> default.

False. There are a few very large record sets on the Internet, and
djbdns has no problem retrieving them. All the djbdns lookup tools
automatically switch from UDP to TCP when necessary.

djbdns supports two configurations for publishing _local_ information:
UDP-only and UDP+TCP. The default configuration is UDP-only, for reasons
explained in http://cr.yp.to/djbdns/faq/tinydns.html#tcp.

> It wouldn't surprise me that this would be a problem with qmail. 

All the popular MTAs have DNS packet size limits. This is BIND's fault:
the BIND resolver interface forces programmers to preallocate DNS packet
buffers.

In contrast, the djbdns client library automatically allocates the right
amount of space for each incoming DNS packet. For the high-level API see
http://cr.yp.to/djbdns/dns.html. qmail 2 will use that API.

---Dan