This Knowledge Base article provides a detailed, technical, and practical guide to configure Proton Mail in Microsoft Outlook and Mozilla Thunderbird.
Unlike traditional email providers, Proton Mail uses end-to-end encryption, which requires a special local application called Proton Mail Bridge to connect desktop email clients. This article explains the architecture, requirements, setup steps, troubleshooting, and security best practices for Proton Mail desktop integration.
This guide is intended for IT administrators, system engineers, and advanced users.
Proton Mail
Proton
Microsoft Outlook
Mozilla Thunderbird
End-to-end encrypted email
Zero-access encryption (provider cannot read emails)
IMAP/SMTP access via Proton Mail Bridge
Custom domains (paid plans)
Secure inbox and attachment encryption
Strong privacy and compliance controls
Open-source cryptography standards
@proton.me
@protonmail.com
@pm.me
All Proton Mail domains use the same Bridge-based configuration.
Proton Mail does not expose standard IMAP/SMTP servers directly because emails are encrypted at rest and in transit.
Proton Mail Bridge:
Runs locally on the user’s system
Decrypts mail locally after login
Provides a local IMAP/SMTP endpoint
Allows Outlook and Thunderbird to function normally
Without Bridge, Outlook and Thunderbird cannot connect to Proton Mail.
| Requirement | Details |
|---|---|
| Proton Mail Plan | Paid plan required (Mail Plus or higher) |
| Proton Mail Bridge | Mandatory |
| Operating System | Windows, macOS, Linux |
| Email Clients | Outlook, Thunderbird |
| Internet | Required for sync |
| Plan | Desktop Client Support |
|---|---|
| Proton Free | ❌ Not supported |
| Proton Mail Plus | ✅ Supported |
| Proton Unlimited | ✅ Supported |
| Proton Business | ✅ Supported |
Proton Mail Bridge is available only on paid plans.
Log in to Proton Mail Web
Go to Settings → All settings → Proton Mail Bridge
Download and install Bridge for your OS
Launch Bridge and sign in with Proton credentials
Unlock mailbox (Bridge runs in background)
After login, Bridge provides local server details (example below):
⚠️ These credentials are not your Proton account password.
Open Outlook
Go to File → Add Account
Choose Manual setup
Select IMAP
Enter Bridge IMAP/SMTP settings
Use Bridge-generated username & password
Enable Outgoing server authentication
Encryption:
IMAP: SSL or STARTTLS
SMTP: SSL or STARTTLS
Save and test send/receive
Open Thunderbird
Click Add New Account → Email
Enter Name and Proton email address
Click Configure Manually
Enter Bridge server details
Authentication method: Normal password
Username & Password: From Bridge
Save configuration and verify sync
Secure desktop email access for privacy-focused users
Corporate environments requiring encrypted email
Compliance-driven communication
Journalists, legal, and research professionals
Migration from web-only to desktop clients
Fix
Ensure Proton Mail Bridge is running
Verify correct local ports
Disable conflicting antivirus email scanning
Fix
Use Bridge-generated credentials
Re-copy username and password from Bridge
Fix
Keep Bridge running in background
Check Proton account storage quota
Fix
Allow localhost (127.0.0.1) connections
Whitelist Bridge application
Bridge decrypts emails only on local machine
Keep OS and Bridge updated
Protect system with disk encryption
Do not share Bridge credentials
Lock Proton session when away
Always start Bridge before Outlook/Thunderbird
Use SSL where possible
Keep Bridge auto-start enabled
Monitor Proton security alerts
Regularly update desktop clients
Avoid public/shared computers
Proton Mail integration with Outlook and Mozilla Thunderbird is achieved securely through Proton Mail Bridge, preserving end-to-end encryption while enabling traditional email client workflows.
For organizations and individuals requiring strong privacy, compliance, and desktop email access, Proton Mail with Bridge provides a reliable and secure solution.
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