How to Upload EML files to Proton Mail Securely?

  

Rollins Duke   
Published: April 7th, 2026 • 4 Min Read

A folder full of EML files may be exported from another email client, saved as backups or collected over time but when you log into Proton Mail, there’s no simple way to import EML to Proton Mail. In this guide, you will learn two proven approaches to easily send email to Proton Mail using a desktop client or a web-based approach. These approaches ensure your emails are properly imported, encrypted and accessible without compromising Proton Mail privacy-first architecture.

Unlike modern email services, Proton Mail doesn’t support direct import of EML files. As a result your email archives remain stuck on your local system and disconnected from your secured inbox.

Why Can’t You Directly Upload EML Files to Proton Mail?

• Proton Mail is designed with end-to-end encryption that means emails must be encrypted when trying to upload.
• Every message is secured using a public encryption key, ensuring you can only read it.
• EML files are raw files stored in MIME format(not encrypted).
• These files are outside Proton Mail’s secure ecosystem and cannot be processed directly.
• Direct upload can bypass client-side encryption and also increase potential security risks.
• This would conflict with Proton Mail’s architecture, as even Proton cannot read EML files.

How to Import EML files to Proton Mail Using Thunderbird?

If you want to import manually then you must have installed both Thunderbird and Proton Bridge and follow the instructions as we have described below:

1. First, download and install Proton Bridge.
2. Download and install Thunderbird on your PC.
3. Now, Sign in to Proton Bridge with your Proton Mail account.
4. Open Thunderbird and add a new email account using Proton Mail Bridge details.
5. Use 127.0.0.1 as the IMAP Server local host.
6. Thunderbird is linked with your Proton Mail account.
7. Then, open your Proton Mail mailbox in Thunderbird.
8. Locate your EML files on your computer and drag and drop into the desired folder in Thunderbird.
9. After synchronization it will reflect on your Proton Mail server.

Drawbacks of the Manual Thunderbird Method

• Proton Bridge is only available with paid plans, this approach is not reliable for free users.
• Dragging thousands of EML files can take lots of hours especially for large EML files.
• Importing too many files can crash Thunderbird or slow down its syncing.
• Users must be friendly with Proton Bridge and Thunderbird to handle this approach.
• The process depends on your PC, if its shutdown unexpectedly or connectivity issues can fail the process.

Special Benefits of Using the EML to Proton Mail Importer

• It allows you to transfer multiple EML files to Proton Mail at once to save time and effort.
• You can easily load batch EML files into your ProtonMail account using secure IMAP credentials.
• With this wizard, you can preserve email integrity including all attachments and formatting.
• This software does not alter the original source files.
• It allows you to transfer emails without data loss or exposure to preserve your ProtonMail accounts.

Conclusion

When importing EML files to Proton Mail then it may seem complicated but when you have the right tools or methods you can make it easier and more secure. After using EML to Proton Mail importer you can easily transfer any number of EML files with preserve their integrity, formatting and attachments.