I use my own domain at $5/year. Their description is a little opaque. I think what they're offering is for them to manage your domain. I set my mail at my regi

I use my own domain at $5/year. Their description is a little opaque. I think what they're offering is for them to manage your domain. I set my mail at my registrar to forward to my fastmail account. I set my client (Thunderbird) to use fastmail's smtp for outgoing, and to identify me as me@mydomain.com in the From: and ReplyTo: fields. Exactly what I did with gmail. Easy Peasy.