Try build 8825.

Are you using an outbound gateway?

No... outbound email is directly delivered without a gateway. 

Upgrade. Its should be solved.

Hi Scot,

Thank you,

The issue may be isolated to domains that have DKIM keys that are 2048 bits long. 2 domains that have keys of 1024 bits appear to be working. 

8825... has anybody seen where to configure DKIM?

I cant find it.....

I configured a 4096 bit key on 8825 and its working.

I have a SmarterMail v15 test server I maintain checkpoints of for this kind of testing, so I reverted it and set up a 768, 1024, and 2048 bit key on three separate domains before verifying they passed DKIM when sending emails. I then upgraded to our latest SmarterMail public release and saw no DKIM issues on signing or in validation on the remote end in my testing. Because we supported custom selectors in previous versions I also tested with and without this involved in the test but couldn't replicate the behaviors you're noting in those tests. I've reached out on a ticket to see if we can collect some diagnostic details from your environment and hope to get to the bottom of this soon!

I am going to try to get this customer to find out who can modify their dns records, and gen a new key in SM. The challenge will be them finding the person who can do that. Thanks to everyone so far 

For anyone else this may help, the DKIM key from v15x did not convert properly. We generated a new 2048 bit key, updated DNS (getting GoDaddy credentials was a whole other problem), and all seems well now. Thanks everyone. We also didn't need to move up to 8825 but will probably do so soon.