<html dir="ltr"><head></head><body style="text-align:left; direction:ltr;"><div>On Fri, 2021-02-26 at 12:03 -0700, Grant Taylor via NANOG wrote:</div><blockquote type="cite" style="margin:0 0 0 .8ex; border-left:2px #729fcf solid;padding-left:1ex"><pre>On 2/26/21 11:46 AM, </pre><a href="mailto:borg@uu3.net"><pre>borg@uu3.net</pre></a><pre> wrote:</pre><blockquote type="cite" style="margin:0 0 0 .8ex; border-left:2px #729fcf solid;padding-left:1ex"><pre>Well, I bet my legacy system will bounce it for example...</pre></blockquote><pre><br></pre><pre>What specifically is the bounce?</pre><pre><br></pre><pre>I thought the purpose of the Null MX was to do two things:</pre><pre><br></pre><pre>1) Provide as an MX that can't be connected to.</pre><pre>2) Serve as a signal to things that know how to interpret it that no </pre><pre>mail is to be expected.</pre><pre><br></pre><pre>I would expect that some server, if not the MSA, /would/ generate a </pre><pre>bounce /because/ the email to the domain is undeliverables.</pre></blockquote><div><br></div><div>Exactly. Postfix bounces it immediately with an accurate message:</div><div><br></div><div><span style="caret-color: rgb(46, 52, 54); color: rgb(46, 52, 54); font-family: monospace;">Domain ???.com does not accept mail (nullMX)</span></div><div><br></div><div>This seems preferable to waiting hours or days for a bounce due to not being able to connect to the A record on port 25 or w/e.</div></body></html>