From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: To: 9fans@cse.psu.edu Subject: Re: [9fans] $smtp dns failure Date: Tue, 16 Jan 2007 15:50:05 -0500 From: geoff@plan9.bell-labs.com In-Reply-To: <81c03baf080b2b71267e6095a9927d2c@coraid.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Topicbox-Message-UUID: 04daf910-ead2-11e9-9d60-3106f5b1d025 When talking about this, it's important to distinguish between the DNS reporting that there is no MX record for a domain and reporting that there is a transient DNS error and thus it can't tell if there is an MX record for a domain. If there is no MX record, smtp should use an A or A6 record, if it exists. If there is a DNS error looking up the MX, smtp should stop and not use any A or A6 record, since that may be the wrong destination, and you can't tell until the transient DNS error passes.