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mail @example.com without dns a-record for example.com

From Salvador Mirzo <smirzo@example.com>
Newsgroups comp.mail.sendmail, comp.mail.misc
Subject mail @example.com without dns a-record for example.com
Followup-To comp.mail.misc
Date 2024-12-22 13:05 -0300
Organization A noiseless patient Spider
Message-ID <878qs7wvmy.fsf@example.com> (permalink)

Cross-posted to 2 groups.

Followups directed to: comp.mail.misc

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Followup-To: comp.mail.misc

The objective here is just learning how things work.  I asked
myself---is it possible to get mail sent to someone@example.com without
an a-record fore example.com?  I think the answer should be ``yes''
because I thought an SMTP would do a type-mx dns query, learn that
example.com mail is handled by mx.example.com, would get the ip address
of mx.example.com and reach the server just fine.

So I made an experiment using my domain---example.com, say.  I've been
geting mail just fine every day.  Then I deleted the a-record for
example.com.  My mail system is not really dependent on it in any way as
far as I know.  So the experiment has the set up:

# host -t a example.com
example.com has no A record

# host -t mx example.com
example.com mail is handled by 10 mx.example.com.

# host -t a mx.example.com
mx.example.com has address 1.2.3.4

But after the deletion of the a-record example.com, I noticed Gmail
seems not to deliver emails to me anymore.  As soon as I created it back
and send a new message, it arrived just fine.

Is is just Gmail or is there more I don't understand?

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Thread

mail @example.com without dns a-record for example.com Salvador Mirzo <smirzo@example.com> - 2024-12-22 13:05 -0300
  Re: mail @example.com without dns a-record for example.com Grant Taylor <gtaylor@tnetconsulting.net> - 2024-12-22 10:36 -0600
  Re: mail @example.com without dns a-record for example.com Claus Aßmann <INVALID_NO_CC_REMOVE_IF_YOU_DO_NOT_POST_ml+sendmail(-no-copies-please)@esmtp.org> - 2024-12-22 12:22 -0500
    Re: mail @example.com without dns a-record for example.com Salvador Mirzo <smirzo@example.com> - 2024-12-23 10:18 -0300
  Re: mail @example.com without dns a-record for example.com kalevi@kolttonen.fi (Kalevi Kolttonen) - 2024-12-22 18:07 +0000
    Re: mail @example.com without dns a-record for example.com Grant Taylor <gtaylor@tnetconsulting.net> - 2024-12-22 22:07 -0600
      Re: mail @example.com without dns a-record for example.com Salvador Mirzo <smirzo@example.com> - 2024-12-23 10:23 -0300
  Re: mail @example.com without dns a-record for example.com John Levine <johnl@taugh.com> - 2024-12-22 21:00 +0000
    Re: mail @example.com without dns a-record for example.com Salvador Mirzo <smirzo@example.com> - 2024-12-23 10:08 -0300
      Re: mail @example.com without dns a-record for example.com Salvador Mirzo <smirzo@example.com> - 2024-12-23 22:01 -0300

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