The Configure Options section of a marketing campaign email lets you select a mail agent for that email - i.e. the address that will be used to send it to the recipients.
You can see a summary of available mail agents in the left-side panel. This will always include the agent associated with the campaign creator, as well as any other mail agents that have been marked as campaign-compatible.
You may wish to use a generic mail agent for your campaign, instead of using your own.
For each email component in a campaign, you can choose to track how many recipients:
Opened the email
Forward the email
Clicked a link within the email