Like many in the community, I had my custom domain hosted with Google right up until they were going to charge me real money. Like many in the community I have iCloud+, so I moved my custom domain over to iCloud.
That was months ago and it just occurred to me that I no longer have a distinct password for my custom domain email. I realized that my rescue email for my Apple ID email was my custom domain email, which means if either one got breached, I’d have no rescue options.
I found a dandy support article at Apple in which they show you how to change your rescue email address. I hopped into appleid.apple.com and changed it to a third address I maintain so now I can sleep at night.
I’m only embarrassed that it took me this long to realize the problem that I could have had!