RE: [PLUG] BIND zone oddity causing SendMail 451 Name server timeout errors?

["kaze" <kaze@voicenet.com>]

--> [mailto:plug-admin@lists.phillylinux.org]On Behalf Of George Theall
--> Sent: Monday, August 02, 2004 10:57 AM

--> While it looks like you've fixed the problem (or at least I can get a
--> response when querying for the A record), you may be interested in the
--> following to explain the behaviour you were seeing:
-->
--> Hostnames used as part of the SMTP MAIL FROM and RCPT TO commands are
--> supposed to be "canonicalized", that is, fully-qualified hostnames or
--> literals rather than nicknames or abbreviations (RFC 821, section 3.1).
--> Yet while the RFC says canonicalization must be done, it's silent in how
--> to actually do it and as a result, the methods used vary from one MTA to
--> another, and even across versions of the same MTA.  For example, older
--> versions of sendmail look for records of type ANY while 8.12.0 and later
--> look first for A records and then either look for MX records if no A
--> records exist or fails if the DNS server itself fails to answer.
--> Postfix, on the other hand, looks for MX records first; if there are
--> none or the DNS server fails *and* ignore_mx_lookup_error is yes, it
--> looks for A records.
-->
--> Hopefully, this explains why failure to get an A record for your hosted
--> domain from your DNS resulted in mail from some but not all
--> hosts getting
--> through.

George, that looks like exactly the description of what was happening. I
haven't gotten any feedback from the L-Users yet insofar as a lack of
delivery failures or delays, OTOH no complaints yet either! Could you share
with us where / how you found this info; both want to read more about it and
want to glean searching/troubleshooting skills - did you just go to the
RFCs? (I guess my subject line was right though.) -Zake

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