We send personal and professional emails everyday and we don't want its content spread across the Internet. However, some email provider companies care more about protecting your data and your privacy than others.
Buried below the mountains in Switzerland, ProtonMail was founded in 2014 at the CERN research unit. ProtonMail uses client-side encryption before emails go through their servers. This means that unlike Gmail, ProtonMail doesn't and cannot read the content of what is being sent. The user base is growing fast, from 2 million (2017) to 5 million (September 2018) until 10 million by the end of 2018.
You can use ProtonMail for free and get 500 MB storage and up to 150 emails per day. For 4 euros per month, you can get the Plus version (5 GB storage, 1000 emails per day).
Posteo is based in the cool city of Berlin in Germany and around since 2009. They support about 300 000 accounts. For 1 euro per month, you can get 2 GB of emails. If you need more GB for all your emails, you can just pay an extra 0.20 euro for every extra GB. They care about your privacy so much that it's actually possible to pay in cash by physical mail.
They have high standards of security and privacy, and support PGP encryption. In addition, their infrastructure runs on 100 per cent clean energy. This way you protect your privacy and the environment.
Tutanota is based in Hamburg Germany and was founded in 2011. It is a free and open-source end-to-end encrypted email software. Tutanota supports over 2 million users (2017). Just like ProtonMail, Tutanota offers end-to-end encryption for emails sent from one Tutanota user to another. When Tutanota users send an email to external recipients, the latter get notified and receive a link to a temporary Tutanota account. The recipient then needs to enter a previously exchanged password and can read the message and reply end-to-end encrypted.
The free account provides 1 GB storage. Premium users can get an expandable 1 GB storage and premium support for 1.20 euro per month. Pro users get 10 GB storage and priority support for 6 euros per month.