Thank you, I meant non-optimal in the sense that using a (possibly free) email provider as a "backend" might mean that the emails are eventually accessible by t

Thank you, I meant non-optimal in the sense that using a (possibly free) email provider as a "backend" might mean that the emails are eventually accessible by third parties. Having your own domain like that mostly shields from the provider locking you out of your email on a whim, but certainly doesn't help much with privacy.