On Saturday, July 2, 2005, 07:28:47, Dan Barker wrote: > There is no way for a non-authorized requestor to find out the hosts of a > domain, but an anonymous requestor can look up a record. So, if you have > mail to [EMAIL PROTECTED], the MTAs will look for an MX > record at accounting.public.domain.tld, and if found, deliver as directed. > Failing that, they will try public.domain.tld, and if found, deliver as > directed. Failing that, they will try domain.tld, and if found, deliver as > directed. Failing that, they will report Unknown Host (although some MTAs > will try for an A record).
I know of no RFC that specifies this behaviour. In RFC 2821 (Simple Mail Transfer Protocol) the first paragraph of section "5. Address Resolution and Mail Handling" specifies Once an SMTP client lexically identifies a domain to which mail will be delivered for processing (as described in sections 3.6 and 3.7), a DNS lookup MUST be performed to resolve the domain name [22]. The names are expected to be fully-qualified domain names (FQDNs): mechanisms for inferring FQDNs from partial names or local aliases are outside of this specification and, due to a history of problems, are generally discouraged. The lookup first attempts to locate an MX record associated with the name. If a CNAME record is found instead, the resulting name is processed as if it were the initial name. If no MX records are found, but an A RR is found, the A RR is treated as if it was associated with an implicit MX RR, with a preference of 0, pointing to that host. If one or more MX RRs are found for a given name, SMTP systems MUST NOT utilize any A RRs associated with that name unless they are located using the MX RRs; the "implicit MX" rule above applies only if there are no MX records present. If MX records are present, but none of them are usable, this situation MUST be reported as an error. There is no mention of successively pruning the FQDN hoping to get a hit. -- [EMAIL PROTECTED] "The avalanche has already started, it is too Rod Dorman late for the pebbles to vote." Ambassador Kosh To Unsubscribe: http://www.ipswitch.com/support/mailing-lists.html List Archive: http://www.mail-archive.com/imail_forum%40list.ipswitch.com/ Knowledge Base/FAQ: http://www.ipswitch.com/support/IMail/
