On 10/09/03 at 15:03, Heath wrote:
Totally baffled by this one.... <head scratch>
Sent a mail to [EMAIL PROTECTED] got a bounce:
Failed to deliver your message to [EMAIL PROTECTED]: SMTP: Unknown domain name Domain Name System has no information about 'mx1.innerprise.net'.
Did host lookup of innerprise.net, got:
innerprise.net has address 69.44.57.238 innerprise.net mail is handled (pri=10) by mx1.innerprise.net
Do host lookup or ping of mx1.innerprise.net and get
unknown host mx1.innerprise.net
There is an MX for innerprise.net that points to mx1.innerprise.net. However, there is no A or CNAME record for mx1.innerprise.net, which makes it kinda hard to use. ;-] This is a problem with innerprise.net's DNS that they should fix.
....yet send a mail via my org's Exchange server and the mail gets through and the user replies!!!!
Exchange is probably falling back to the A record for innerprise.net, which does have an MTA that answers on port 25. SIMS is obviously not trying it, presumably because there is an MX record. Someone with better knowledge of the RFCs can tell us which is the correct behavior.
If there is an MX record, falling back to an A record for the name is never correct. An MX which points to a name that has no A is a misconfiguration that has to be fixed for any standards-complaint mail server to deliver to that domain.
The fallback to A records only exists because MX records are a late addition to how mail is routed, and Internet standards are developed by processes that avoid breaking backwards compatibility. The behavior before MX records existed was to just use the A records, and any domain with no MX records might conceivably still be operating under the old norms. Falling back to A records in that case supports backwards compatibility. A domain with an MX record pointing at an unresolvable name clearly is operated by someone aware of the 'new' (an invention of the 80's) MX record and who wants to NOT have mail aimed at the A record. Fallback in that case does not support any sort of past normal practice.
-- Bill Cole [EMAIL PROTECTED]
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