All emails stored on Proton Mail’s servers are protected by end-to-end encryption(new window) or zero-access encryption(new window), so no one — not even Proton — can access their contents. This also prevents us from sharing your emails with your email client.
Email clients such as Microsoft Outlook, Mozilla Thunderbird, and Apple Mail use the IMAP(new window) and SMTP(new window) protocols to receive, manage, and send emails. IMAP and SMTP secure emails in transit using encryption standards such as TLS(new window). However, they aren’t designed to access emails stored using zero-access encryption.
Since IMAP can’t decrypt your emails, the email server needs to access them unencrypted. This means you can’t configure your client to connect directly with Proton Mail.
Proton Mail Bridge solves this problem. With Proton Mail Bridge installed on your computer, you can access your Proton Mail emails using your regular desktop email client while also maintaining end-to-end or zero-access encryption.
Proton Mail Bridge downloads the emails from your Proton Mail account and decrypts them locally so your email client can access them.
To achieve this, Proton Mail Bridge creates IMAP and SMTP servers on your computer. These run in the background when you launch Bridge, and are accessible only to applications running on the same device.
This allows your email client to connect with your Proton Mail account, with Bridge taking care of encrypting emails when you send them and decrypting emails when you receive them.
This tight integration between Proton Mail Bridge’s IMAP and SMTP servers and your email client provides a seamless experience, while also ensuring that your data remains secure and private at all times.