A reader clicks the Forward button in the footer of your campaign.
They enter up to 5 friends' email addresses for forwarding.
They can include a short personal message.
Then they click the Forward button, and see a message saying:
YOUR EMAIL WAS SUCCESSFULLY FORWARDED.
Those friends of your original recipient will receive your campaign with the personal note included, above it -- just like when forwarding a regular email. Your forwarded recipients can see everything in your original campaign, so it makes sense to include a call to action to subscribe.
On your stats page, you can see how many times the original campaign was forwarded, and by which original recipient. You can't see the contact emails that were forwarded to -- they'll have to subscribe first!