I am running an Exchange 2013 with about 10 domain names.

I currently use DynDNS' backup MX service - which covers a single domain per license. I want to look into creating my own backup MX service in the cloud (Azure?) so that I can restart my Exchange server when needed without having to worry about having emails bounced (for all current and future domains).

What is the best way of going about this?

  • 1
    The value of having a backup MX is a debatable proposition. If your Exchange server is down for a short period of time then the sending server MUST queue the message for later retries. Messages to your domains will not bounce, they will be queued for later retries and will be delivered once your Exchange server is backup, unless the retry intervals have expired. Every email server I've ever worked with has a maximum retry interval of two days.
    – joeqwerty
    Dec 27, 2013 at 16:16
  • @joeqwerty - did it change over time? I recall the default retry being 4 days.
    – TheCleaner
    Dec 27, 2013 at 16:28
  • @joeqwerty - I like having secondary MX's because I prefer to have delivery complete successfully to a machine I control, rather than having to wait for the sender's server to resend. It's probably because I'm a control freak, but I like to be able to "see" the mail waiting in a queue that I can dequeue on-command, versus having to tell the Customer "let's just wait for mail to come in" after getting the primary MX working again. Dec 27, 2013 at 16:28
  • In addition to what Evan answered, You can use various 3rd parties as well, such as Spamsoap, etc. that are cheap and will also do logging/scrubbing/maintenance queuing, etc.
    – TheCleaner
    Dec 27, 2013 at 16:30
  • I had thought that I had tested having my server down and I was getting bounces immediately - but it was awhile back so I am not sure. IF that is truly the case than there really isn't any point to having a backup MX server - especially when I only have 50 or so mailboxes ATM.
    – William
    Dec 28, 2013 at 3:09

1 Answer 1


It really depends on your comfort level with SMTP MTA software.

The built-in Windows SMTP server would also do what you need. Create an instance on an off-premise server and create "remote domains" for each of the domain names you need to accept mail for. Then, configure those domains to smart-host to your primary MX.

The SMTP server in "modern" versions of Windows runs as an IIS 6 component, so you'll have to install the IIS 6 management tools. Most of the documentation that I'm finding is Windows 2003-centric, however the configuration should be the same even on newer versions of Windows.

You could also do something exceedingly inexpensive with various free / open-source MTAs if you're willing to put the time into configuring them.

  • Interesting idea - I am going to dig into this further
    – William
    Dec 28, 2013 at 3:10

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