Dropbox offers a software product where you can store, synchronize and share files online with public access. This free trial onboarding email sequence is used to persuade people to subscribe for Dropbox pro.
Dropbox opens with an invitation where you can subscribe for the free version of Dropbox. Followed by some instruction emails, including an invitation to download Dropbox on your other devices. After this they suggest to update your Dropbox to the Dropbox pro version. They use urgency to convince you to upgrade, by telling you your Dropbox is almost full. If you decide to upgrade, they will send a follow up email, promoting the Dropbox Pro Yearly Plan.
You can read more about Dropbox here: https://www.dropbox.com