Exchange 2013 Hybrid, Cloud Migration

Hi Guys

I have a couple of questions regarding a cloud migration. First is what are people using for a mail relay when they migrate to the cloud?. We have various systems that fire emails off to a SMTP service on one of our mailbox servers, this will need replacing somehow.

And the other is, what DNS changes do i need to make internally so our outlook clients look to the Exchange Online instance, im presuming autodiscover but i havent really looked into it yet.

Cheers

Julian