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

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  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

#1202 — mail @example.com without dns a-record for example.com

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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#1203

On 12/22/24 10:05, Salvador Mirzo wrote:
> Is is just Gmail or is there more I don't understand?

Per RFCs, email is supposed to prefer the MX record and the host name 
therein.

Gmail does things by their own rules.

My only question is, does the MX record also get removed when you remove 
the A record?  I've seen questionable DNS administrative interfaces 
remove the entire record, not just the specific resource record.



-- 
Grant. . . .

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#1204

Salvador Mirzo  wrote:

> The objective here is just learning how things work.  I asked

You might want to read the fine RFCs, e.g., RFC 5321
5.1.  Locating the Target Host
....
   The lookup first attempts to locate an MX record associated with the
   name. [[...]]

> 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''

Correct.

> But after the deletion of the a-record example.com, I noticed Gmail

Since you haven't given real data it's hard to say what you did
wrong. Maybe your MX record is incorrect or hasn't propagated yet.

-- 
Note: please read the netiquette before posting. I will almost never
reply to top-postings which include a full copy of the previous
article(s) at the end because it's annoying, shows that the poster
is too lazy to trim his article, and it's wasting the time of all readers.

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#1209

Claus Aßmann
<INVALID_NO_CC_REMOVE_IF_YOU_DO_NOT_POST_ml+sendmail(-no-copies-please)@esmtp.org>
writes:

> Salvador Mirzo  wrote:
>
>> The objective here is just learning how things work.  I asked
>
> You might want to read the fine RFCs, e.g., RFC 5321
> 5.1.  Locating the Target Host
> ....
>    The lookup first attempts to locate an MX record associated with the
>    name. [[...]]

Thank you so much for the reference.

>> 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''
>
> Correct.
>
>> But after the deletion of the a-record example.com, I noticed Gmail
>
> Since you haven't given real data it's hard to say what you did
> wrong. Maybe your MX record is incorrect or hasn't propagated yet.

I was likely confused---I updated you all in a follow-up to John Levine.

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#1205

In comp.mail.sendmail Salvador Mirzo <smirzo@example.com> wrote:
> [...] 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?

The email standards do not require a-record so this must
one of Gmail's quirks.

br,
KK

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#1207

On 12/22/24 12:07, Kalevi Kolttonen wrote:
> The email standards do not require a-record ...

Not for the domain name with the MX record.

But there needs to be an A and / or AAAA record for the FQDN that the MX 
record references.

> ... so this must one of Gmail's quirks.

I wonder if this might be a Google'ism wherein they saw / cached an A 
record and are now cross that there isn't one.  <something> <something> 
security <something> false test result.



-- 
Grant. . . .

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#1210

Grant Taylor <gtaylor@tnetconsulting.net> writes:

> On 12/22/24 12:07, Kalevi Kolttonen wrote:
>> The email standards do not require a-record ...
>
> Not for the domain name with the MX record.
>
> But there needs to be an A and / or AAAA record for the FQDN that the
> MX record references.

Here's a passage from RFC 5321 that confirms this:

   --8<-------------------------------------------------------->8---
   5.1.  Locating the Target Host

   Once an SMTP client lexically identifies a domain to which mail will
   be delivered for processing (as described in Sections 2.3.5 and 3.6),
   a DNS lookup MUST be performed to resolve the domain name (RFC 1035
   [2]).  The names are expected to be fully-qualified domain names
   (FQDNs) [...]

   [...]

   When a domain name associated with an MX RR is looked up and the
   associated data field obtained, the data field of that response MUST
   contain a domain name.  That domain name, when queried, MUST return
   at least one address record (e.g., A or AAAA RR) that gives the IP
   address of the SMTP server to which the message should be directed.
   --8<-------------------------------------------------------->8---

>> ... so this must one of Gmail's quirks.
>
> I wonder if this might be a Google'ism wherein they saw / cached an A
> record and are now cross that there isn't one.  <something>
> <something> security <something> false test result.

Thanks for bringing that up.  It turns out it just confusion on my part.

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#1206

If you want help, you need to tell us the actual domain.  Otherwise we'd
just be guessing what you did.

According to Salvador Mirzo  <smirzo@example.com>:
>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?


-- 
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly

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#1208

John Levine <johnl@taugh.com> writes:

> If you want help, you need to tell us the actual domain.  Otherwise we'd
> just be guessing what you did.

Thank you---I appreciate that!  The domain is antartida.xyz.  So I
deleted the a-record again.  Now we have:

%host -t a antartida.xyz
antartida.xyz has no A record

%host -t mx antartida.xyz
antartida.xyz mail is handled by 10 mx.antartida.xyz.

%host -t a mx.antartida.xyz
mx.antartida.xyz has address 195.88.57.140

%host -t ptr 195.88.57.140
140.57.88.195.in-addr.arpa domain name pointer mx.antartida.xyz.

What do I see now?  I see I was confused before because I *am* getting
e-mails from Gmail.  What stopped working for me is my IMAP client that
for some reason is not seeing the messages arrive after I deleted the
a-record of antartida.xyz, but then I tried another client and it sees
them all, so it's a client (Gnus) configuration issue.  (That's another
investigation I need to make, but it's not important.)  I apologize for
the confusion.

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#1211

Salvador Mirzo <smirzo@example.com> writes:

> [...] What stopped working for me is my IMAP client that
> for some reason is not seeing the messages arrive after I deleted the
> a-record of antartida.xyz, but then I tried another client and it sees
> them all, so it's a client (Gnus) configuration issue.  (That's
> another investigation I need to make, but it's not important.)  I
> apologize for the confusion.

I had two fetchmailrc (for no good reason) and I updated the wrong one.
After finding the right one and updating the hostname to
mx.antartida.xyz, I also had to get a new certificate to match the new
hostname.  Then my fetchmail was able to pull mail once again and
deliver it to my IMAP server to tell Gnus (my reader) that I indeed have
new mail.  (Yes, I plan to simplify this as soon as possible.  I need to
learn more about everything.)

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