This is something most useful and usable thing in daily life. Everyone using email service with a concern of "security".
Now that the solution 'Tutanota'.

Pros:-

• open source service, anyone can creatively improve the codes.
• more user attracted as it is open source software.
• compatible for both of Android and iOS platform.
• end to end encryption provide effective users privacy security, it is the most important thing today.
• simple UI make it user friendly.
• all that great advantages are for free.

Cons:-

• limited 1 GB storage space. You have to pay for premium or pro service for more storage space and more facilities. (Well it's logical.)