[ALUG] Correct MX record configuration

Simon Ransome simon at nosher.net
Mon Feb 20 11:46:41 GMT 2017


On 20/02/17 10:47, Laurie Brown wrote:
> On 19/02/17 21:53, Chris Green wrote:
>> This may relate to my recent long question about loss of E-Mail.
>>
>> Can anyone tell me *exactly* how an MX record for my home server
>> zbmc.eu should be confiugured?
>>
>> Currently it's configured to point to the 'root' A record for zbmc.eu,
>> so the MX record is for zbmc.eu also:-
>>
>>     chris at cheddar$ host zbmc.eu
>>     zbmc.eu has address 84.92.49.234
>>     zbmc.eu mail is handled by 10 zbmc.eu.
>>     chris at cheddar$ 
>>
>> However I *think* this may be wrong and I should create a second A
>> record for the same IP address and point the MX record to that
>> instead.  I don't really understand why this should make any
>> diffrerence though.
>>
>> Any experts (or at least people who know more than me) here?
> 
> I define them thus:
> 
> @convergent-ict.com::mg3.convergent-ict.com:10:86400
> @convergent-ict.com::mg5.convergent-ict.com:10:86400

<snip>

Hi Chris,

By way of further explanation...

The "10" in the above example is the MX Preference (it's an arbitrary
number between 0 and 65535 but where 10 has become something of a
rule-of-thumb). Here this means that as the two MX records have the same
preference, any incoming connections should (in theory) load-balance
between the two servers, mg3 and mg5. However, in the case of your
original configuration, where it sounds like there is only one host,
there would be no point creating a second A or MX record as it would be
pointing to the same server anyway.

Another common example is to set up your own host with an MX Pref of 10
and an ISP host with a higher number, say 100 - this routes mail mostly
to your own server but gives it a backup route to your ISP if yours is
unavailable.

cheers,
Simon




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