RE: Mail Routing Question

[Kevin Miller]

Good catch.  I was trying to be succinct, but didn't realize that one couldn't 
use an IP rather than the hostname.  

So the corrected example should be something like this then:

mailIN A 192.168.0.2
aaa IN A 192.168.1.1
IN MX 10 mail.aaa.com. 


...Kevin
--
Kevin Miller
Network/email Administrator, CBJ MIS Dept.
155 South Seward Street
Juneau, Alaska 99801
Phone: (907) 586-0242, Fax: (907) 586-4588 Registered Linux User No: 307357

-Original Message-
From: owner-postfix-us...@postfix.org [mailto:owner-postfix-us...@postfix.org] 
On Behalf Of /dev/rob0
Sent: Thursday, November 16, 2017 5:57 PM
To: postfix-users@postfix.org
Subject: Re: Mail Routing Question

On Thu, Nov 16, 2017 at 10:43:16PM +, Kevin Miller wrote:
> You can point the A record for aaa.com to one IP and the MX record for 
> it to another.

Yes, but not as per your example.

> I.e.
> aaa   IN A 192.168.1.1
>  IN MX 10 192.168.1.2

The RDATA for MX is "integer hostname".  In your example the "192.168.1.2" 
would be read as a hostname, and noting the lack of trailing dot, the zone 
file's current $ORIGIN value would be appended.

> In the example above, a web page to http://aaa.com would go to 
> 192.168.1.1, whereas an SMTP server would connect to 192.168.1.2.

In this example mail would most likely not be deliverable.  The MX record in 
DNS would point to a name which probably does not exist.
--
  http://rob0.nodns4.us/
  Offlist GMX mail is seen only if "/dev/rob0" is in the Subject:

Re: Mail Routing Question

[/dev/rob0]

On Thu, Nov 16, 2017 at 10:43:16PM +, Kevin Miller wrote:
> You can point the A record for aaa.com to one IP and the MX record 
> for it to another.

Yes, but not as per your example.

> I.e.
> aaa   IN A 192.168.1.1
>  IN MX 10 192.168.1.2

The RDATA for MX is "integer hostname".  In your example the 
"192.168.1.2" would be read as a hostname, and noting the lack of 
trailing dot, the zone file's current $ORIGIN value would be 
appended.

> In the example above, a web page to http://aaa.com would go to 
> 192.168.1.1, whereas an SMTP server would connect to 192.168.1.2.

In this example mail would most likely not be deliverable.  The MX 
record in DNS would point to a name which probably does not exist.
-- 
  http://rob0.nodns4.us/
  Offlist GMX mail is seen only if "/dev/rob0" is in the Subject:

Re: Mail Routing Question

[Doug Hardie]

> On 16 November 2017, at 14:45, Viktor Dukhovni  
> wrote:
> 
> 
> 
>> On Nov 16, 2017, at 5:32 PM, Doug Hardie  wrote:
>> 
>> I have a domain, say: aaa.com for which I receive mail.  Currently I have A 
>> records in DNS for aaa.com and mail.aaa.com as well as a MX record for 
>> aaa.com.  All three of them point to the same IP address which is where 
>> postfix is running.  There is a political issue with the A record for 
>> aaa.com and it "needs" to be changed to elsewhere.  I somehow seem to recall 
>> that there are some MTAs that do not use the MX records, but only check the 
>> A records.
> 
> Any MTA that fails to check MX records is badly broken, and can barely
> deliver email to any domains that matter (all the big players have
> MX hosts separate from their A/ records used primarily for HTTP).
> 
>> Will changing the A record for aaa.com cause the loss of some incoming mail
> 
> No.
> 
> -- 
>   Viktor.
> 

Thanks to all.  I have changed the A record.  

Re: Mail Routing Question

[Benny Pedersen]

Doug Hardie skrev den 2017-11-16 23:32:

Will changing the A record for
aaa.com cause the loss of some incoming mail?


no, if that changed ip accept delivery of that recipient domain

back to what mx does ?, it only defines a seperate hostname to deliver 
mail to if mail and other servicefs on hostnamea is not same as service 
on hostnameb eq if you only have single ip, do not use mx setup


people are misguided if that say mx is needed to recieve emails, i have 
seen fool bounces that i need mx to recieve bounces, where the bounced 
text was rejected mail from me since i did inded not have a mx, i dont 
need a complex world setup for a single ip

Re: Mail Routing Question

[Viktor Dukhovni]

> On Nov 16, 2017, at 5:32 PM, Doug Hardie  wrote:
> 
> I have a domain, say: aaa.com for which I receive mail.  Currently I have A 
> records in DNS for aaa.com and mail.aaa.com as well as a MX record for 
> aaa.com.  All three of them point to the same IP address which is where 
> postfix is running.  There is a political issue with the A record for aaa.com 
> and it "needs" to be changed to elsewhere.  I somehow seem to recall that 
> there are some MTAs that do not use the MX records, but only check the A 
> records.

Any MTA that fails to check MX records is badly broken, and can barely
deliver email to any domains that matter (all the big players have
MX hosts separate from their A/ records used primarily for HTTP).

>  Will changing the A record for aaa.com cause the loss of some incoming mail

No.

-- 
Viktor.

RE: Mail Routing Question

[Kevin Miller]

You can point the A record for aaa.com to one IP and the MX record for it to 
another.

I.e.
aaa IN A 192.168.1.1
 IN MX 10 192.168.1.2

All the MX record does is tell the world what mail host to use for a given 
domain.  So you may have a web server running on aaa.com but not your email 
server.  When someone queries aaa.com the A record is normally returned, but if 
the type is set to MX then the MX record is returned instead.

In the example above, a web page to http://aaa.com would go to 192.168.1.1, 
whereas an SMTP server would connect to 192.168.1.2.

Be sure that you update the PTR records for the hosts when you change them...

...Kevin
--
Kevin Miller
Network/email Administrator, CBJ MIS Dept.
155 South Seward Street
Juneau, Alaska 99801
Phone: (907) 586-0242, Fax: (907) 586-4588 Registered Linux User No: 307357


-Original Message-
From: owner-postfix-us...@postfix.org [mailto:owner-postfix-us...@postfix.org] 
On Behalf Of Doug Hardie
Sent: Thursday, November 16, 2017 1:32 PM
To: Postfix users
Subject: Mail Routing Question

I have a domain, say: aaa.com for which I receive mail.  Currently I have A 
records in DNS for aaa.com and mail.aaa.com as well as a MX record for aaa.com. 
 All three of them point to the same IP address which is where postfix is 
running.  There is a political issue with the A record for aaa.com and it 
"needs" to be changed to elsewhere.  I somehow seem to recall that there are 
some MTAs that do not use the MX records, but only check the A records.  Will 
changing the A record for aaa.com cause the loss of some incoming mail?

-- Doug

Mail Routing Question

[Doug Hardie]

I have a domain, say: aaa.com for which I receive mail.  Currently I have A 
records in DNS for aaa.com and mail.aaa.com as well as a MX record for aaa.com. 
 All three of them point to the same IP address which is where postfix is 
running.  There is a political issue with the A record for aaa.com and it 
"needs" to be changed to elsewhere.  I somehow seem to recall that there are 
some MTAs that do not use the MX records, but only check the A records.  Will 
changing the A record for aaa.com cause the loss of some incoming mail?

-- Doug