Re: [mailop] Is Yahoo! breaking the RFC 5321 for an Implicit MX?

[Kurt Jaeger]

Hi!

> have an explicit null MX record in the DNS, e.g.:
> 
> foo MX 0 .
> 
> See RFC 7075.

That's RFC 7505.

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Re: [mailop] Is Yahoo! breaking the RFC 5321 for an Implicit MX?

[Philip Paeps]

On 2017-04-19 12:36:23 (+0200), Philip Paeps  wrote:
On 2017-04-19 12:15:06 (+0200), David Hofstee 
 wrote:
It may have to do with squatted/parked domains and/or port 25 being 
closed by a firewall. Parked domains generally have A records for 
showing ads but often do not have MX records (or an open port 25). 
Instead of getting a bounce immediately, you may have to wait for a 
timeout when the sender makes a simple typo.


And then there are cases when parked domains do have port 25 open 
and/or an MX record. Different discussion.


The correct way to indicate that a domain does not accept email is to 
have an explicit null MX record in the DNS, e.g.:


   foo MX 0 .

See RFC 7075.


RFC 7505 actually.  Lack of caffeine causes slydexia. :o

Philip

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Re: [mailop] Is Yahoo! breaking the RFC 5321 for an Implicit MX?

[Philip Paeps]

On 2017-04-19 12:15:06 (+0200), David Hofstee  
wrote:

2017-04-19 3:50 GMT+02:00 John Levine :

In article <92c77841-5260-5c05-c3e6-56671eeb2...@pccc.com> you write:
However, under RFC 5321, section 5.1, I had always thought that 
without an MX, the system should revert to using the A record as an 
implicit MX.


You are correct.

On the other hand, these days domains that expect mail generally do 
have MX records, so I can't blame them for treating the lack of MX as 
a signal that the address is bogus.


It may have to do with squatted/parked domains and/or port 25 being 
closed by a firewall. Parked domains generally have A records for 
showing ads but often do not have MX records (or an open port 25). 
Instead of getting a bounce immediately, you may have to wait for a 
timeout when the sender makes a simple typo.


And then there are cases when parked domains do have port 25 open 
and/or an MX record. Different discussion.


The correct way to indicate that a domain does not accept email is to 
have an explicit null MX record in the DNS, e.g.:


   foo MX 0 .

See RFC 7075.

Philip

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Philip Paeps
Senior Reality Engineer
Ministry of Information

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Re: [mailop] Is Yahoo! breaking the RFC 5321 for an Implicit MX?

[David Hofstee]

It may have to do with squatted/parked domains and/or port 25 being closed
by a firewall. Parked domains generally have A records for showing ads but
often do not have MX records (or an open port 25). Instead of getting a
bounce immediately, you may have to wait for a timeout when the sender
makes a simple typo.

And then there are cases when parked domains do have port 25 open and/or an
MX record. Different discussion.


David Hofstee
OpenText

2017-04-19 3:50 GMT+02:00 John Levine :

> In article <92c77841-5260-5c05-c3e6-56671eeb2...@pccc.com> you write:
> >However, under RFC 5321, section 5.1, I had always thought that without
> >an MX, the system should revert to using the A record as an implicit MX.
>
> You are correct.
>
> On the other hand, these days domains that expect mail generally do
> have MX records, so I can't blame them for treating the lack of MX
> as a signal that the address is bogus.
>
> R's,
> John
>
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>



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