I've been on the "Enhanced" plan for years now and have at least a dozen domains and maybe a dozen and a half email addresses configured. FM will also let you

I've been on the "Enhanced" plan for years now and have at least a dozen domains and maybe a dozen and a half email addresses configured. FM will also let you (if not encourage you to) to use its DNS servers instead of your registrar's, but that's up to you. I generally use FM for DNS hosting but you absolutely do _not_ need to do this to host domain mailboxes with them.