Pros;

1. Being an open source product, it gives it more chance of growth and improvement through users suggestions
2. It gives highly reputable companies the opportunity to communicate privately to their clients.
3. It is fast and more flexible than the existing mail services.
4. Being a cloud app, your data is secured and can't get lost.

Cons:

1. The Storage allowed would limit users from picking it over other mailing service.
2. The premium prices are high compared to the privacy service they are offering.