Resend is a service for sending email. Once you connect it, your assistants can see what you sent recently and draft the next campaign with that history in mind. Nothing goes out until you press Approve.
The Marketing assistant is the one that works with campaigns. Like every persona except the Coder, it is Coming soon. Once Resend is connected, the connection is also visible to the CEO assistant, so it can brief the right assistant when you ask for a campaign.
Reading your recent sends and drafting a campaign needs no Approve. Drafts live in your StellarFirm workspace until you decide.
Sending is a step that reaches other people, so it always stops at your Approve, even when other categories are set to Auto-approve in Settings. Sending also stays off until you allow it, so connecting Resend alone never lets an assistant send.