I don't need a custom domain anymore and I find it trivial to change email addresses. I can use 1password to locate accounts, easily migrate, apply a tag, and work through the change over a few hours. I typically change email every 2-3 years and it serves as a good way to review security settings/change passwords. Modern email providers have mailbox porting tools, and they work fine. I use to like having a domain, but dunno, for a privacy nut, seems more secure to not use one.