ProtonMail Bridge an application that runs on your computer in the background and encrypts and decrypts your mail as it enters and leaves your computer. It allows for full integration of ProtonMail accounts with any program that supports IMAP and SMTP such as Microsoft Outlook, Mozilla Thunderbird and Apple Mail.
ProtonMail finally released the long awaited ProtonMail Bridge to support email clients like Apple Mail, Thunderbird and Outlook on Mac and Windows.
Pros:IMAP support for native email clients.
Cons:Does not support Linux yet. Bridge is available for paid members only.