Pros:

• Provides encrypted mailbox for free.
• It's an open source and forever free.
• It has a strong encryption type service
• You can easily communicate with any of your friends end-to-end encrypted.
• It is available in web browsers so that you can view your mailbox anywhere and it is available in mobile apps both Android and iOs.

Cons:

• Bigger storage is available only in pro version.
• Nothing more I can see at the moment