On 23/Sep/10 01:00, Malcolm Weir wrote:
>>From: Ben Kennedy [mailto:[email protected]]
>
>>With respect, I still find this argument somewhat specious.  Virtually
>>every enterprise of any size on the internet still runs multiple MX
>>servers.  While I appreciate that having a single point of reception
>>means a simpler configuration, it also foregoes some measure of
>>redundancy and versatility.  Are Google and Apple and IBM and the White
>>House out of their minds?  I suppose that perhaps Courier is the wrong
>>product for any such business, but if so, it seems an unfortunate design
>>exclusion.  In any case, that's getting off track.
>
> In my experience, enterprises of size actually operate dedicated boundary
> servers as their MX platforms, and final delivery is handled by an entirely
> different set of servers often totally invisible to the outside user.

While that's correct, those invisible servers are not _primary_ MXes 
on the public Internet.  So, it is still unanswered why large 
enterprises may want to operate _secondary_ MXes, i.e. MXes with a 
higher preference number.

It is possible to have multiple primary MXes (each one possibly 
multi-homed).  For example, the White House doesn't seem to have 
secondary MXes:

;; QUESTION SECTION:
;whitehouse.gov.                        IN      MX

;; ANSWER SECTION:
whitehouse.gov.         10800   IN      MX      105 mail1.eop.gov.
whitehouse.gov.         10800   IN      MX      105 mail2.eop.gov.
whitehouse.gov.         10800   IN      MX      105 mail3.eop.gov.
whitehouse.gov.         10800   IN      MX      105 mail4.eop.gov.

(The same is true for ibm.com, but not for apple.com and gmail.com.)

I agree that out-of-the-box Courier is the wrong product for a 
businesses running backup MXes, just like any other standard compliant 
SMTP server.  The reason is that the traditional (non-filtering) 
design of secondary MXes is broken.  This rules out the possibility of 
outsourcing backup MXes, which would be the most interesting solution 
for servers confined within a single RIR.

-- 
http://fixforwarding.org/wiki/Backup_MX







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