Proton Mail IMAP Settings: Why There Is No Public IMAP Server

If you searched for Proton Mail IMAP settings and expected to find a hostname, a port, and a password — the kind of details you'd enter into Thunderbird or Apple Mail in under two minutes — you're about to learn that the situation is different. The settings exist, but they don't point to a remote server.

Proton Mail has no public IMAP or SMTP server. You cannot point an email client at imap.proton.me and connect. This is not a missing feature or a temporary gap. It is a direct consequence of how Proton stores your mail. Every message sits on Proton's servers in encrypted form that the server itself cannot read. Standard IMAP requires the server to hand over message content in plaintext — something Proton's architecture deliberately prevents.

The only supported path to IMAP access is Proton Mail Bridge, a desktop application that runs on your own machine. Bridge decrypts your mail locally and exposes a private IMAP and SMTP server that listens only on 127.0.0.1. That is the host address — not a remote hostname. This post explains the architecture, walks through the configuration, and is clear about one limit that affects cloud-based email tools in particular.

Why Proton Mail Has No Public IMAP Server#

A standard email provider — Gmail, Outlook, Fastmail, almost any other — stores your messages in a format the server can read on demand. When an email client connects via IMAP, the server fetches the message, formats it, and sends it over the wire. The provider can do this because they hold the mail in a form they can access.

Proton Mail was built around the opposite model. Messages are encrypted on your device before they leave it, using keys that only you hold. By the time a message reaches Proton's servers, it is already ciphertext. Proton cannot decrypt it — not because they chose not to, but because the decryption key never reaches their infrastructure in the first place. This is what zero-knowledge encryption means in practice: the server is blind to your message content.

Standard IMAP cannot work in this environment. RFC 9051 defines IMAP as a protocol for accessing and manipulating messages stored on a server. But if the server cannot read those messages, it cannot serve them via IMAP. A real imap.proton.me endpoint would require Proton to hold decryption keys, which would invalidate the privacy guarantee at the product's core.

Bridge is the architectural workaround. It runs on your desktop, authenticates to Proton's API using your credentials, downloads the encrypted mail, and decrypts it locally using the keys stored on your device. It then presents that decrypted content through a private IMAP server listening on 127.0.0.1. Your email client connects to Bridge. Bridge connects to Proton. There is no public server in between.

What You Need Before You Start#

Bridge has specific requirements, and the most important one blocks more setups than any configuration step: it is available only on paid Proton plans. You cannot use Bridge on a free Proton account, regardless of which desktop operating system you are running. Before installing anything, confirm you have each of the following.

• A paid Proton Mail plan. The free tier does not include Bridge access. This is a hard requirement with no workaround on the Proton side.
• A supported desktop operating system. Bridge runs on Windows 10 or later (64-bit), macOS 10.15 Catalina or later, and most major Linux distributions. It does not run on iOS or Android — mobile Proton Mail access is only available through Proton's own mobile apps.
• The Bridge installer from proton.me/mail/bridge. Download it directly from Proton. Do not use third-party sources.
• An email client that accepts manual IMAP configuration. Proton has tested Bridge with Thunderbird, Apple Mail, and Outlook. Any client that lets you enter a custom IMAP host and port should work.
• Your Proton account credentials. Bridge will prompt you to sign in when you first launch it, after which it generates the separate Bridge password you will use in the client.

How to Configure Your Email Client with Proton Mail Bridge#

Once Bridge is installed and running, the configuration process is the same regardless of which email client you use. The steps below assume Bridge is open and you have signed in to your Proton account inside it.

1. 1

   Install and open Bridge

   Download Bridge from proton.me/mail/bridge and run the installer for your operating system. Open Bridge and sign in with your Proton account credentials — your regular Proton email address and password. Bridge authenticates to Proton and begins building a local index of your mailbox. For large accounts this takes several minutes.

2. 2

   Copy the Bridge-generated password

   Inside Bridge, select your account. You will see a password field showing a long generated string — this is not your Proton account password. Copy it. You will paste this into your email client in a later step. Bridge may let you regenerate it if needed; if you do, any existing client connections using the old password will stop working until you update them.

3. 3

   Open your email client and start adding a new account

   In Thunderbird, go to Account Settings and choose to add a new email account. In Apple Mail, go to Mail then Add Account. In Outlook, go to File then Add Account. When the client offers to detect settings automatically, decline — choose manual IMAP setup. Automatic detection will fail because 127.0.0.1 is not a publicly routable host.

4. 4

   Enter the IMAP settings

   For the incoming server, set the host to 127.0.0.1 and the port to 1143. Choose STARTTLS for the encryption method. Enter your full Proton Mail address as the username and paste the Bridge-generated password. Do not use SSL/TLS on port 993 — Bridge does not listen on that port in its default configuration.

5. 5

   Enter the SMTP settings

   For the outgoing server, set the host to 127.0.0.1 and the port to 1025. Choose STARTTLS for encryption. Use the same full Proton Mail address and the same Bridge-generated password as the incoming server. Click finish or save and allow the client to test the connection.

6. 6

   Wait for initial sync

   The first sync downloads and indexes your Proton mailbox through Bridge. For accounts with years of mail this can take several hours. Bridge must keep running in the background for the email client to send or receive. Closing Bridge while the client is open will cause connection errors.

Proton Mail IMAP and SMTP Settings Reference#

Here are the exact values to enter in any email client. These apply to a default Bridge installation. If you changed Bridge's port numbers to resolve a conflict, substitute the ports you set.

Where Bridge Works and Where It Does Not#

The settings above work on any desktop platform that Bridge supports. Mobile platforms and hosted email services are a different matter entirely. The table below shows where Bridge can and cannot reach.

What to Do When Bridge Is Not Working#

The most frequent reason Bridge fails to connect is not a configuration mistake — it is the wrong password. The Bridge-generated password and your Proton account password look nothing alike and are not interchangeable. If your email client returns an authentication error on the first attempt, open Bridge, copy the generated password again, and paste it fresh into the client's password field.

The second most common problem is a port conflict. If another application on your machine is already using port 1143 or 1025, Bridge reports a port occupied error and cannot start its local server correctly. Open Bridge, go to Settings, then Advanced settings, then Default ports, and increment the conflicting port by one — for example, from 1143 to 1144. Update the matching value in your email client to stay in sync.

• Authentication failed: confirm you are using the Bridge-generated password, not your Proton login. Open Bridge, copy the generated password for your account, and re-enter it in the client.
• Port already in use: go to Bridge Settings, Advanced settings, Default ports, and increment the conflicting port by one. Update the email client to the same new port number.
• Connection refused: confirm Bridge is actually running. The local IMAP and SMTP servers only exist while Bridge is open and signed in. On some machines Bridge does not start automatically after a reboot.
• Certificate or SSL mismatch: the client may be trying SSL/TLS on port 993 or 465. Switch to STARTTLS on port 1143 for IMAP and port 1025 for SMTP.
• Mailbox empty or sync stalled after setup: Bridge indexes messages progressively. Large mailboxes can take several hours to fully appear. Leave Bridge running and check again the following day before troubleshooting further.

A Faster Way for Other Email Accounts#

Everything above works — Bridge is the correct, supported path for accessing Proton Mail in a third-party desktop client. It has one structural limit: Bridge runs on your machine. The local IMAP server it exposes listens only on 127.0.0.1, so it is reachable only from that same machine, and only while Bridge is open.

If you also manage accounts on Gmail, Outlook, Fastmail, or any provider that exposes a standard remote IMAP server, AI Emaily connects to those directly — no Bridge, no local daemon. We build AI Emaily. It is a hosted email client with an AI assistant that triages your inbox, drafts replies based on the voice and context you define in your Personal Context, and handles routine correspondence at the autonomy level you set, from manual approval to Autopilot with undo and a full audit log. It does not connect to Proton Mail, because Bridge's local-only architecture makes that technically impossible for any hosted service. But if your non-Proton accounts are where you want AI-assisted inbox management, the AI email assistant handles that across Gmail, Outlook, and IMAP providers directly.