Proton has released a desktop version of the ProtonMail app, giving users full access to ProtonMail and ProtonCalendar, and (eventually) the ability to view emails offline. The desktop app, currently in beta, has been optimized for Windows and macOS and will encrypt sent emails end-to-end like the browser version, while offline access to email will be available "soon" according to the Swiss company.
Accessing Proton email offline via the desktop email application is technically possible, but your account must be configured using the Proton Mail Bridge to work with other IMAP/SMTP email clients such as Microsoft Outlook, Apple Mail, etc. Proton's desktop app, on the other hand, lets you access your email offline without having to set up a mail bridge, which should be more convenient. (Proton says the program will cache large amounts of email for offline use).
It’s important to note that sending and encrypting emails on Proton still requires internet access. But offline functionality lets you check and draft emails while traveling, having a power outage, or other situations where you don't have access to the Internet.
Proton also provides encrypted automatic forwarding services for paying users, including desktop and browser versions, but forwarding encryption only applies to emails forwarded to other Proton users. The company said it has also made improvements to ProtonCalendar, including a fully searchable web version.
Not everyone will have immediate access to Proton's desktop app. Proton is first restricting access to its paid "Visionaries" package to traditional users (although the company will reopen subscriptions to this package until January 3, 2024). The desktop application is planned to be available to all users in early 2024.