ProtonMail is an end-to-end encrypted email service, adding an extra layer of security on top of traditional email messaging. The additional security features means you can't connect a ProtonMail account to a third-party email application, like you can with Gmail or Yahoo accounts. ProtonMail's solution to this is the ProtonMail Bridge application, which has been around for a while, but has now received a significant update.

ProtonMail wrote in a blog post, "We have redesigned ProtonMail Bridge to offer you a better overview of your account(s) and revamped our Settings so you can now easily control the location of your cache or reset the app. It also comes with dark mode! [...] This new version of ProtonMail Bridge is packed with fixes and improvements, but the main change is the new local cache, which now includes full message bodies. This means ProtonMail Bridge stores messages encrypted on your device, so they can be retrieved much faster than when stored remotely on our servers."

ProtonMail Bridge, as the name implies, acts as a bridge between an email client running on a computer and ProtonMail's servers. The utility sets up a local mail server that mail clients can connect to, and end-to-end encryption is maintained between ProtonMail and the local server. That way, you can use applications like Thunderbird or Apple Mail with a ProtonMail account, while also using those clients with other accounts. However, the bridge still isn't available for mobile platforms, so people on iOS or Android are still tied to the official ProtonMail mobile applications.

ProtonMail Bridge is available to download for Windows, macOS, and Linux (in both DEB and RPM package format). The update is slowly rolling out to anyone with ProtonMail Bridge already installed, but you can also force the update by downloading the installer again. Unfortunately, ProtonMail Bridge still does not run natively on Apple M1-powered Mac computers.