A friend of mine used to say "people who shoot from the hip often end up losing toes." I think I lost a metaphorical toe on Friday.
After a bit of a postmortem with Squarespace support, it's become clear that I was wrong in my assessment that Squarespace automatically grabs your email when you point your domain to it. Actually, the default behavior is to route web browsing to your site, but leave your mail routing intact. I discussed the domain mapping process with Squarespace support in detail, and it's clear that their process only involves CNAME and A records that affect web browsing. In fact they avoid editing MX (mail exchange) records so as not to disrupt your email. So, what happened in my case?
When I first went to hook my Squarespace site up to my domain on Friday, I thought that I should be hooking up to GoDaddy (where the domain was originally registered) but my DNS records were actually being managed by BlueHost (where the previous version of my site was being hosted). When I saw that Squarespace was finding BlueHost instead of GoDaddy, my knee-jerk reaction (the shoot from the hip moment) was to switch the DNS back to GoDaddy. It's likely that doing so deleted the DNS pointer that connected my domain to the BlueHost mail servers. That's where my trouble began. Next, I pointed the GoDaddy nameservers at my Squarespace site. To do this, GoDaddy applies what it calls a "template." I suspect because the pointer to BlueHost's mail servers had been stripped away, the template pointed the mail to Squarespace by default.
After a few minutes, it dawned on me that this was incorrect, so I tried to revert to the arrangement I had before — I moved the DNS management back over to BlueHost, thinking that the mail would reconnect. It probably didn't. When I mapped Squarespace onto the BlueHost DNS, the records now contained the incorrect MX pointer to the Squarespace servers. Unfortunately, it took three rounds of corrections over about 4-1/2 days to resolve.
I've heard back from one friend that he got some bounces saying that his messages could not be delivered. That's actually reassuring. The worst would be to have people send me messages and neither of us has any notion that the message didn't get through.