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We have had some issues with losing internet connection once in a while. Normally that would mean our mail server is unreachable and incoming email is bouncing. We've set up MX Backup (second MX record after ours) and while for some providers it was enough (gmail dropped to second MX and was able to queue up mail), others still bounced the email (hotmail).

Is there anything we can do to make sure that we never lose email? We would like to host email internally because there is a lot of internal email traffic. We are also considering a backup internet connection (what would be the proper dns/mx setup for that)? Still even with backup we sometimes lose power so having email queued outside would be perfect but backup MX doesn't seem to be reliable enough.

Please let me know what's possible in our situation to improve email reliability.

Thanks.

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If you setup your second MX and some messages where getting bounced, then perhaps you need to investigate more into why that is happening. A backup MX should work correctly. –  Zoredache Oct 25 '10 at 17:25
    
As I mentioned some providers bounce the messages, others don't and send it to the secondary MX record. Not sure what else I can investigate here. –  Zero Cool Oct 25 '10 at 17:46
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3 Answers

up vote 4 down vote accepted

You can never be sure you'll not lose email. That's just not in the protocol.

However, properly configured email servers will try again for something like 12 to 48 hours, with longer and longer windows between retry attempts rather than just dropping the email altogether.

Technically you can't control what other mail servers do or if they're configured properly. Part of the problem in my experience is that people are of the mentality that email is instant messaging. It's not. It's unreliable and rickety and it's amazing that it is still usable in this day. There's nothing built in for authenticating or verifying users, it's not encrypted, and because of spammers, it's not uncommon for legit messages to get stuck in junk folders or for email servers to drop messages suspected of being spam without notifying the sender that the message wasn't truly delivered.

If you already have a second MX record to an off-site host, you're already doing the right thing. The next thing you could try is setting up redundant links with two different providers and play with BGP and the wonderful and unique world of hurt that playing with redundant links brings.

The real question is, that for this downtime, did it affect your mail and business to the point that it justifies pursuing this route? How often do you experience outages, and how long do they typically last? If the business impact is high enough you can look at the redundancy route; otherwise maintain an offsite (with separate provider) second MX system and that should be good enough until the benefit/cost ratio dictates otherwise.

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That's the conclusion I came to and I guess I was afraid hoping that I was wrong. Downtimes don't happen that often but as usual when they do happen it's the most important email for the business that gets lost :) What would be proper setup for network redundancy? Would I create round robin A record and use that as my MX record or is protocol for that different? Thanks –  Zero Cool Oct 25 '10 at 17:45
    
For network redundancy? You'd have to investigate the two links using two different providers and use BGP to route. It's a slightly different bag of crazy to deal with (en.wikipedia.org/wiki/Multihoming). You'll probably want to ask another question separate from this if you want to investigate network availability using multiple providers. –  Bart Silverstrim Oct 25 '10 at 21:21
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You could use a solution like postini, since its now owned by Google, you can leverage their spam filtering, and also have a place for mail to queue if your connection goes down that your Exchange server is on. I've used it in the past, and it was fantastic when the datacenter that we had our Exchange servers at was experiencing issues.

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We don't want to move to an external mail system because of heavy internal traffic, we don't want internal traffic to go outside. Thanks –  Zero Cool Oct 25 '10 at 17:47
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Internal MAPI traffic will NEVER go through an outside source, it will stay inside the Exchange server. –  DanBig Oct 25 '10 at 17:48
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Another service like Postini is mailroute.net. One advantage of services like Postini and mailroute is that you also get spam and virus filtering allowing you to, in many cases, significantly reduce mail volumes to your network.

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