I've got a question about it : protonmail encrypt my email, but if i send an email to gmail or yahoo, my email won't be secure ?
It is useless to use protonmail if i don't send emails to protonmail adresses ?
Thanks
From ProtonMail:
Messages are encrypted at all times
1> Messages are stored on ProtonMail servers in encrypted format. They are also transmitted in encrypted format between our servers and user devices. Messages between ProtonMail users are also transmitted in encrypted form within our secure server network. Because data is encrypted at all steps, the risk of message interception is largely eliminated.
2> ProtonMail's zero access architecture means that your data is encrypted in a way that makes it inaccessible to us. Data is encrypted on the client side using an encryption key that we do not have access to. This means we don't have the technical ability to decrypt your messages, and as a result, we are unable to hand your data over to third parties. With ProtonMail, privacy isn't just a promise, it is mathematically ensured. For this reason, we are also unable to do data recovery. If you forget your password, we cannot recover your data.END
It will till it hits their inbox brother and you also have the option to send self-destructing messages.
But yeah you may be right, it's not for everyone.
You may find an option out there that better suits your needs.

PeAcE