There’s an understanding in the security community that security and convenience are at opposite ends of the same spectrum when it comes to technology. Since opening up to the public last year, the CERN developed ProtonMail has been decidedly leaning into the security end of the email spectrum. The benefit was it provided robust end-to-end encryption on email. The downside was you were limited to their webmail client, or dedicated smartphone apps. For someone with multiple accounts living in another email client, it was definitely not the most convenient.
However the recently released ProtoMail Bridge makes some concessions to bring their robust encryption in a slightly more convenient way. The bridge app is installed on a local machine, and essentially acting as a mail server that decrypts email for your client of choice to read. This lets you get all the same search and multi-account access you’d expect from a modern email client, but when you send or receive email from ProtonMail, you get the same secure encryption.
Now the downside of this is that this makes your mail vulnerable to end-point attacks. Like I said, security and convenience are almost always a trade off. But I think you’re not losing much security in exchange for a much more usable solution. It seems weird that ProtonMail adding a man-in-the-middle actually contributes to a more secure solution, but there you have it.