Getting Exchange to do DKIM

Question

Having read Jeff's blog post about Email and DKIM, I'm thinking it might be good to DKIM all mail coming out of our Exchange 2003 servers. Whats a good way of going about that?

Solution 1

No version of Exchange supports DKIM. Microsoft has put their support behind SPF/SenderID instead. There are a couple third-party products that can be added to Exchange to do DKIM (like this, for instance) but I personally wouldn't run that stuff on any of my Exchange servers. The more common approach is to have another server (or servers) sitting between Exchange and the internet running a more secure MTA that can do the DKIM for you.

Solution 2

I wrote an open source DKIM signing module for Exchange 2007, 2010, 2012, and 2016: https://github.com/Pro/dkim-exchange

We are using it now for a few months and didn't have any problems yet.

Solution 3

I have an open source version of a DKIM signing transport agent for Microsoft Exchange hosted on BitBucket here. It only works on Exchange 2007 at the moment, although it could easily be adapted to work on later versions. Unfortunately 2003 can't be helped because there is no ability to write your own transport agents on it.

Comments

[joeqwerty]

While I agree with you on your DKIM statements, I disagree with your insinuation that Exchange's MTA isn't secure. It's not the MTA that's insecure it's the admins who don't configure Exchange correctly that makes it insecure.

[John Gardeniers]

Too bad about Microsoft's attitude on this, as things like SPF and DKIM are complementary, not in opposition. Quite simply, having both lowers the spam score more than having just one of them on all the test systems I've seen so far, as well as the production spam filters I've looked at.

[Tory Netherton]

UPDATE: I highly recommend using the project mentioned by Probot (github.com/Pro/dkim-exchange) instead of that little one I made.