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Setting up pop3 and smtp failover

Posted on 2013-06-07
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Last Modified: 2013-06-15
I currently have 2 mail servers running on 2 different isp's, with 2 different outside ip addresses. They are located on the same network and I am able to connect the two so that they share settings, email, etc. I want to setup a load balance/failover situation where if one goes down the end client doesn't notice a change. I have read and am under the impression that this can be done through round robin dns and mx record priority. I understand how this will allow other email servers to connect to mine for email transport but my question is how will the end user be affected?

For example, if I setup my clients to use get.email.com for their incoming and outgoing servers and have get.email.com dns records point to my two outside ip addresses, what will happen if one of my servers goes down? Will it try the other ip in the dns record? In other words how will the email client behave if the first ip address that is resolved is down?
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Question by:goatbeater
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Expert Comment

by:kevinhsieh
ID: 39250118
Round robin DNS won't work, because a client that receives the bad IP address won't try again with the other address. You need a service such as the one provided by DNSMadeEasy.com where they can detect that the service is down on one IP and then change the DNS record to point to a different IP. You still want to use multiple MX records for inbound email.

I have used DNS Made Easy for about five years now and have been very happy with their service.
http://www.dnsmadeeasy.com/services/dns-failover-system-monitoring/
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Author Comment

by:goatbeater
ID: 39250166
I have looked at a couple of dns services. My concern with them is the time it would take for the dns records to update and replicate through the internet to the client. Also I have my domain with register.com, would a service like dnsmadeeasy work with them our would I need to move it?
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kevinhsieh earned 2000 total points
ID: 39250194
You need to move just the DNS service, or change the record to a cname and point to a host name in a new domain that you use a different DNS provider for. You can set the ttl down to 60 seconds, which works pretty well.

The face is that Pop3 clients don't have a built in mechanism for high availability. Unless you plan on investing in a global load balancer solution, DNS is all you have.
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Expert Comment

by:eeRoot
ID: 39250481
DNS can hand out multiple IP addresses, but it has no idea if an email sever is up and running or not, so it will keep on directing connections to a downed server.  There are load balancers that can intelligently track which servers are up and down.

http://www.zenloadbalancer.org/
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