In version 1.16 ProtonMail released it’s latest push to provide a private email service. With the goal of giving our users full (and exclusive) control of their data, we implemented encrypted attachments. Every time an attachment is received by a ProtonMail account it is encrypted. Attachments are encrypted by default between ProtonMail and ProtonMail correspondence; however, from ProtonMail to non-ProtonMail correspondence it is not end to end encrypted at this time (coming soon). When a message from a non-ProtonMail account enters the ProtonMail system it is immediately encrypted with the recipients public key, ensuring it is stored encrypted with the recipient being the only person with a key to decrypt it.
This process of encrypted attachments requires the latest browser technology. The latest versions of both Chrome and Firefox support this technology flawlessly; however, Safari does not. At this time, most safari users can right click on the attachment and save the attachment. The file name will not be saved and will show up in your downloaded files at “unknown”. Some attachments may have their extensions removed using Safari. We are working on making this process as seamless as possible; and, as always, we recommend you try a different browser if you are having trouble.