I added DMARC and DKIM together, around the same time as some particular life events 10 years ago. Just now, I cross-checked the information against the commits in my Git repos.

Back then, I didn’t use Terraform or anything like that, but I had text files with logs that described the DNS setup in detail so I could fix things. By grepping through the logs, I’m able to put a definitive bound on when I added DMARC—it was no later than June 2016, over 10 years ago.

At the time I thought, “Obviously, we should all be setting this up, because recipients will start rejecting mail from insecure domains, if they don’t already.” This was also back when I self-hosted email. I eventually stopped doing that because I thought it was too time-consuming.