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X-Original-To: nanog@nanog.org X-Really-To: <nanog@nanog.org> In-Reply-To: <CAO0-hXYohUsZmGSANEaOx78ggekN1BoYvhZjv20AnSzwKyFcOg@mail.gmail.com> From: William Herrin <bill@herrin.us> Date: Mon, 15 Jun 2015 15:15:51 -0400 To: Joe Hamelin <joe@nethead.com> Cc: "nanog@nanog.org" <nanog@nanog.org> Errors-To: nanog-bounces@nanog.org 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/>
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