It is a MUST as the lookup succeeds. Also from RFC2821: When the lookup succeeds, the mapping can result in a list of alternative delivery addresses rather than a single address, because of multiple MX records, multihoming, or both. To provide reliable mail transmission, the SMTP client MUST be able to try (and retry) each of the relevant addresses in this list in order, until a delivery attempt succeeds.
> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On > Behalf Of David, Andy > Posted At: Thursday, January 13, 2005 10:26 AM > Posted To: swynk > Conversation: undeliverable domain > Subject: RE: undeliverable domain > > > I think we can all agree that having a mx record is a > GoodThing and having a mailer that will fall back to an A > record is a GoodThing as well if it cant find a mx. > Note that Symantec will also not deliver if it finds a CNAME. > As far as I can tell however the "implicit MX" rule is not a > MUST either. > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On > Behalf Of Michael B. > Smith > Sent: Thursday, January 13, 2005 11:08 AM > To: Exchange Discussions > Subject: RE: undeliverable domain > > OK, Chris pulled out the OLD RFC so I thought to pull out the > current one. > :-) > > RFC 2821, section 5: > > 5. Address Resolution and Mail Handling > > 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. "implicit MX" 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. > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On > Behalf Of Michael B. Smith > Sent: Thursday, January 13, 2005 11:01 AM > To: Exchange Discussions > Subject: RE: undeliverable domain > > That's not the RFC rule. > > The RFC requires attempted delivery to the "A" record if no > "MX" records exist. > > I didn't look it up, but I sure could. It's in either RFC > 2821 or RFC 2822. > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On > Behalf Of Martin Blackstone > Sent: Thursday, January 13, 2005 10:49 AM > To: Exchange Discussions > Subject: RE: undeliverable domain > > That must be the party line excuse because I hear that as well. > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf > Of Jonathan Beeler > Sent: Thursday, January 13, 2005 7:27 AM > To: Exchange Discussions > Subject: RE: undeliverable domain > > It's safe to say that the product sucks. My company got it > in the Symantec enterprise "Suite", effectively for free. > > I'm trying to convince them to use a linux mail host running > sendmail - as I've been doing for the last while - but to no avail. > > Symantec's line is that they go by strict RFC rules - my > reply, was that's fine, but what about the real world rules? > > Anyway, thanks for the input. > _________________________________________________________________ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Web Interface: http://intm-dl.sparklist.com/read/?forum=exchange > To subscribe: http://e-newsletters.internet.com/discussionlists.html/ > To unsubscribe send a blank email to > [EMAIL PROTECTED] > Exchange List admin: [EMAIL PROTECTED] > To unsubscribe via postal mail, please contact us at: > Jupitermedia Corp. > Attn: Discussion List Management > 475 Park Avenue South > New York, NY 10016 > > Please include the email address which you have been contacted with. > > _________________________________________________________________ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Web Interface: http://intm-dl.sparklist.com/read/?forum=exchange > To subscribe: http://e-newsletters.internet.com/discussionlists.html/ > To unsubscribe send a blank email to > [EMAIL PROTECTED] > Exchange List admin: [EMAIL PROTECTED] > To unsubscribe via postal mail, please contact us at: > Jupitermedia Corp. > Attn: Discussion List Management > 475 Park Avenue South > New York, NY 10016 > > Please include the email address which you have been contacted with. > > > _________________________________________________________________ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Web Interface: http://intm-dl.sparklist.com/read/?forum=exchange > To subscribe: http://e-newsletters.internet.com/discussionlists.html/ > To unsubscribe send a blank email to > [EMAIL PROTECTED] > Exchange List admin: [EMAIL PROTECTED] > To unsubscribe via postal mail, please contact us at: > Jupitermedia Corp. > Attn: Discussion List Management > 475 Park Avenue South > New York, NY 10016 > > Please include the email address which you have been contacted with. > > > _________________________________________________________________ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Web Interface: http://intm-dl.sparklist.com/read/?forum=exchange > To subscribe: http://e-newsletters.internet.com/discussionlists.html/ > To unsubscribe send a blank email to > [EMAIL PROTECTED] > Exchange List admin: [EMAIL PROTECTED] > To unsubscribe via postal mail, please contact us at: > Jupitermedia Corp. > Attn: Discussion List Management > 475 Park Avenue South > New York, NY 10016 > > Please include the email address which you have been contacted with. > > > _________________________________________________________________ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Web Interface: http://intm-dl.sparklist.com/read/?forum=exchange > To subscribe: http://e-newsletters.internet.com/discussionlists.html/ > To unsubscribe send a blank email to > [EMAIL PROTECTED] > Exchange List admin: [EMAIL PROTECTED] > To unsubscribe via postal mail, please contact us at: > Jupitermedia Corp. > Attn: Discussion List Management > 475 Park Avenue South > New York, NY 10016 > > Please include the email address which you have been contacted with. > > > _________________________________________________________________ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Web Interface: http://intm-dl.sparklist.com/read/?forum=exchange To subscribe: http://e-newsletters.internet.com/discussionlists.html/ To unsubscribe send a blank email to [EMAIL PROTECTED] Exchange List admin: [EMAIL PROTECTED] To unsubscribe via postal mail, please contact us at: Jupitermedia Corp. 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