Exchange only service - DNS Settings

Hi,

We are setting up a new Office365 account for a company that currently has its own domain running a public web site.

They wish to purchase the "Email (exchange online)" only plan £2.82 pu/pm.

My question relates to the method they have to use to setup DNS for their external web site.  I have a E3 account and have to do it via my domain registrar, i have seen the small business accounts have to do it via Office365 DNS.

What method do people who only buy the Email service have to use.

Thanks,

David.