The following Marketo features are required to be able to use Jeto.
Marketo REST API with sufficient bandwidth\limits for your campaign volume. Jeto will typically use 175-500 API per campaign, including reviews/update (the default limit was 10k calls per day at the time or writing this article).
Although not required, these are highly recommended Marketo features for an optimal experience:
Marketo Secured Domains enabled for Landing Pages, Images and Files (SSL/HTTPS)
The use of Agical other advanced "add to calendar" solution is recommended. This will help overcome limitations of the native Marketo function and allow Jeto to automatically generate these links for you via tokens.