If you were to move your root domain to our Cloud platform, you can add whatever DNS records you need to it (so long as they don't conflict with what we need to host your community 🙂 ) . If you were to use a sub-domain here on our Cloud platform, you remain in control over your DNS, we just supply you what you need to point the sub-domain here.
In sending email out from your community, we have our own Cloud email sending service that is provided as a part of your package. If that is not something you want to use, you can still use the same options available to you on self-hosted, SendGrid or SMTP (or a third party application API).