D. J. Bernstein <d...@cr.yp.to> wrote: > My "qmail" software is very widely deployed (on roughly 1 million SMTP > server IP addresses) and, by default, relies upon ANY queries in a way > that is guaranteed to work by the mandatory DNS standards.
There are three bugs in the way qmail uses ANY queries. (1) qmail uses ANY queries for domain canonicalization on outgoing messages, as specified by RFC 1123. But canonicalization is not required by the current SMTP specification. It is a waste of time. Fixing this bug would make bug (3) moot. (2) qmail's DNS response buffer is too small to accommodate a complete DNS message, so it fails if it gets a large response. It uses the low-level libc resolver API which can easily handle large responses, including fallback to TCP, so it is a pity that qmail breaks this part of the resolver's functionality. This bug means it is not guaranteed to work. (3) Using an ANY query suppresses alias processing, so qmail makes a series of queries to follow CNAME chains. This is inefficient and wasteful. If you make an A or MX query, the DNS server will chase the CNAME chain for you, so you only need to make one query to get the canonical name. Tony. -- f.anthony.n.finch <d...@dotat.at> http://dotat.at/ Trafalgar: Easterly 5 or 6 in far southeast, otherwise northerly 4 or 5. Moderate or rough. Mainly fair. Good. _______________________________________________ DNSOP mailing list DNSOP@ietf.org https://www.ietf.org/mailman/listinfo/dnsop
