The fastest and easiest way to send end-to-end encrypted email in ProtonMail is to have both ends of the conversation use ProtonMail. In emails between ProtonMail accounts, the PGP encryption takes place automatically behind the scenes, with no technical expertise required.
However, if using ProtonMail is not an option for your contacts, there are two other methods to send end-to-end encrypted email in ProtonMail: Encryption for Outside Users or external PGP encryption.
External PGP encryption is an advanced ProtonMail feature that allows you to send encrypted emails to non-ProtonMail email addresses using the recipient’s public key. This feature is also supported in the Bridge, but it requires some additional configuration in the web app.
Adding your recipient’s public key
Setting up encryption so that ProtonMail automatically encrypts messages sent to a specific non-ProtonMail recipient can either be done by manually uploading the public key of the recipient into ProtonMail’s contacts manager or by asking the contact to send you an email with their public key attached.
Instructions to add your contact’s public key can be found in our article “How to use PGP” under the subheading Sending PGP emails. We recommend also reading the entire article before using PGP in ProtonMail.
It is not possible to do this within your mail client or in the Bridge. To add a recipient’s public key to their contact, you must log into your ProtonMail account at mail.protonmail.com.
Once you have added the recipient’s public key, you can send them emails normally and they will be encrypted automatically.
Unencrypted outgoing email notification
The Bridge application can also let you know if the message you’re sending to a non-ProtonMail email address is not encrypted (i.e. you have not added a public encryption key to the contact). This option is disabled by default, but you can enable it by going to Bridge -> Settings and toggling the “Notification of outgoing email without encryption” button.
When enabled, you will receive a pop-up alert after pressing Send on an email to one or more recipients with no encryption settings. You will have the opportunity to cancel the outgoing message by clicking on “Cancel”. Or you can send the message by clicking “Send now” or by waiting five seconds, at which point the message will be sent.