Exchange Server Send connector and DNS Round Robin ?

Hi All,

If I create two different IP address (A) record for the Linux appliance in my internal DNS server and then make it the same name like below:

External AD-Integrated DNS server:
mail.domain.com (A Record) 202.43.252.167 Default TTL 1 hr.
mail.domain.com (A Record) 202.43.252.91 Default TTL 1 hr.

Internal AD-Integrated DNS server:
mail.domain.com (A Record) 10.1.1.100 Default TTL 1 hr.
mail.domain.com (A Record) 10.1.11.113 Default TTL 1 hr.

PRODMAIL01-VA.domain.com (A Record) 10.1.1.100
PRODMAIL02-VA.domain.com (A Record) 10.1.11.113

Would that configuration works for the Exchange Server 2013 Send Connector resiliency if I just put mail.domain.com ?

So if I need to perform maintenance or upgrade on the Virtual appliance, I can just delete the (A) record and then retype it again once it is done, without causing any email queue or blockage.

My assumption is that the TTL in the public DNS can be reduced to just 1 minute to expedite the process when the email is queued during the appliance maintenance.

Any help and comment would be greatly appreciated.
LVL 9
Senior IT System EngineerIT ProfessionalAsked:
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Chris DentPowerShell DeveloperCommented:
it doesn't, by itself, offer resiliency. If an attempt to send leads to one A record, and that fails, the mail service will not try the other one.

If you're going to pull / push records as and when you need (and with awareness of the TTLs) them it'll be fine.
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Senior IT System EngineerIT ProfessionalAuthor Commented:
OK, so how to make it resilient by using DNS round robin ?
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Chris DentPowerShell DeveloperCommented:
Resilient / DNS round robin... These things don't fit together at all in any automatic sense.

If you're looking at this to provide resilience you have to consider it as you did in the first place: Low TTL and change / remove records if something is going offline.

If you need it to be automatic you need to think in terms of load balancers, or at the very least something to monitor services and carry out the DNS changes for you.
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Senior IT System EngineerIT ProfessionalAuthor Commented:
Chris, so in my case here it would be better off just to use each appliance IP address (A) record than the mail.domain com ?
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Chris DentPowerShell DeveloperCommented:
The send connector accepts more than one smart host when you define the connector. I would imagine that this is somewhat fault tolerant and it'll try all of them until it works or there are no more to try. This might be the safest path, routing stays strictly with Exchange in that scenario.
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Senior IT System EngineerIT ProfessionalAuthor Commented:
Thanks, Chris.

So I assume that I leave the both IP address like the two lines above, then Exchange will intelligently pick which one is up.
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