[ALUG] Correct MX record configuration

Chris Green cl at isbd.net
Mon Feb 20 18:41:46 GMT 2017


On Mon, Feb 20, 2017 at 11:46:41AM +0000, Simon Ransome wrote:
> 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.
> 
I did basically understand most of this.  Though adding a lower
priority alternative is something I might add so that turning my
system off for a while won't hurt (though of course senders should in
theory back off and try again).

No on seems to have quite understood my original query though - is it
OK for the mail server to point directly at the main/root host?

-- 
Chris Green



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