Re: Anycast provider for SMTP?

[William Herrin <bill () herrin us>]

On Mon, Jun 15, 2015 at 2:13 PM, Joe Hamelin <joe () nethead com> wrote:
> The two MX sites are connected via third party MPLS.  The problem is when
> one MX site loses Internet connectivity the sending MTA may take up to 4
> hours to resend and hopefully the DNS coin toss gives it the address of the
> site that is still connected.

Hi Joe,

Have you been able to document which originating MTA software
misbehaves this way? Correct SMTP behavior is to attempt TCP
connections to all IP addresses at each MX level in turn, and repeat
for each MX level. Only upon failure of all of them. defer the message
for later delivery.

Interrupted connections (as opposed to timeouts) may go straight to
deferred, figuring that bulk traffic like email should pause if
congestion exhibits itself in the form of a stalled TCP connection. So
it would make sense for a handful of messages to be delayed. And of
course all bets are off if Internet connectivity is "flapping" instead
of hard down.

Regards,
Bill Herrin


-- 
William Herrin ................ herrin () dirtside com  bill () herrin us
Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>