We configure ours for two reasons: most mailers will retry immediately on some connection errors (even as late as starttls or helo) but only if you have "more" hosts/ips for them to try. With load balancers, there's no other way to tell remote servers to try again quickly. I assume this is similar at least to what you're talking about.
The other thing is that we vend an ip to the dns request based on load/availability and closeness to the requestor. Our alt addresses vend other data centers down the list, which helps move the traffic in the first minutes of unavailability before the automated systems catch up and the dns ttl expires. We've considered switching away from this. The added benefit is pretty low, and there is some benefit to having fewer simpler entries for gsuite customers. Ah, we also used multiple mx to roll out changes. Ie, when we rolled out ipv6 addresses, we added it on a higher pref mx first. Brandon On Thu, Dec 17, 2020, 1:25 PM John Levine via mailop <mailop@mailop.org> wrote: > As we all know, MX records have a priority number, and mail senders > are supposed to try the highest priority/lowest number servers first, > then fall back to the lower priority. > > I understand why secondary MX made sense in the 1980s, when the net > was flakier, there was a lot of dialup, and there were hosts that only > connected for a few hours or even a few minutes a day. > > But now, in 2020, is there a point to secondary servers? Mail servers > are online all the time, and if they fail for a few minutes or hours, > the client servers will queue and retry when they come back. > > Secondary servers are a famous source of spam leaks, since they > generally don't know the set of valid mailboxes and often don't keep > their filtering in sync? What purpose do they serve now? > > R's, > John > > PS: I understand the point of multiple MX with the same priority for > load balancing. The question is what's the point of a high priorty > server that's always up, and a lower priority server that's, I dunno, > probably always up, too. > > > > _______________________________________________ > mailop mailing list > mailop@mailop.org > https://list.mailop.org/listinfo/mailop >
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