How to Import EML to Office 365 Without Losing Attachments (2026)

Published By Jamie Kaler

Approved By Rollins Duke

Published On June 8th, 2026

Reading Time 11 Min Read

Looking for a safest way to import EML to Office 365? Multiple users feel the need to perform EML to Office 365 migration due to the requirement to move or archive emails to Microsoft 365. In this guide we will discuss manual as well as automated methods to open EML in Office 365 while maintaining the integrity and preserving all the associated attachments, folder structure and email metadata.

Your data is precious and this is what we prioritize the most. Migrating your data from one place to another can affect the data integrity the most. Users generally ask can Office 365 open EML files directly? or how many EML files can be imported at once in Office 365? And we will discuss each and everything that you need to know about the EML to Office 365 migration as well as each and every aspect of the process with safety.

Let us move forward and before jumping to the process let’s discuss why users even need to import EML to Office 365?

What is EML and Office 365

EML is a standard file format that is used to save individual email messages and acts like a digital envelope, saving the email’s subject, body, sender/receiver email addresses, date, and all the associated attachments.

Office 365 is Microsoft’s cloud-based Exchange Online email, and also a classic application such as Microsoft Word, Excel, OneDrive. It stays in your local hard drive and exists on Microsoft’s servers that helps to synchronize smoothly across all devices.

Quick Help: How to Import EML to Office 365?

What We Have Analyzed: While we were working on an internal testing, our team imported more than 5,000 EML files in a Microsoft 365 mailbox. But by the time we realized that the Outlook-based imports were generally time-consuming as all the desired emails had to be moved individually. Thunderbird handled batches better but it required some additional configuration. Whereas, a direct migration software preserved folder hierarchy and reduced the time and effort for the entire process.

Why Does a User Need to Open EML file in Office 365?

The EML to Office 365 migration process basically consolidates scattered, standalone emails into a secure centralized cloud environment. Below are some basic yet powerful reasons to import EML files to Office 365 environment.

Professional Email Management: It is useful to import EML to Office 365 as the Microsoft 365 platform makes it easier for users to manage all the scattered folders/files across one platform for better organization and accessibility.
Enhanced Security: Microsoft 365 supports professional grade security features such as encryption, threat protection, and Multi-factor authentication. This helps protect confidential information and ensures that previously stored emails remain secure.
Easy Accessibility: Office 365 is a cloud platform that can be easily accessible through any device with an internet connection. So, users don’t have to be dependent on their computer system to read the EML data.
Advanced Search Capabilities: Microsoft 365 provides advanced and powerful search features using which users can easily find the required EML files, attachments and other data without having to open each file individually.
Collaboration & Future Proofing: Storing EML files in Office 365 makes it easier for users to share, forward and collaborate important conversations. Also, it ensures that your data is compatible and accessible within the modern cloud based environment.

Can Office 365 Import EML Files in bulk Directly?

Office 365 does not natively support importing .eml files in bulk as its cloud platform and Exchange Online requires synchronizing data or typical .pst files for all types of import tasks. However, Users can use some manual techniques or any reliable workaround depending on the total number of files they actually need to process.

Preparations Before EML to Office 365 Migration

These are some important steps that every user should take before starting with any method. So, make sure:

You have a stable internet connection throughout the process.
Install and set up Outlook or Thunderbird email clients.
Arrange all EML files in one place in folders to maintain them in a structured way and avoid missing any email.
Always perform a small migration test with a few emails before going with the entire data.
Create a backup of all EML files and keep them saved at a separate place.
Ensure Office 365 mailbox has sufficient space to store all email messages.

How to Import EML to Office 365 Manually?

Let’s discuss the real manual ways to open EML files in Microsoft 365 using desktop-based services like Outlook and Thunderbird.

Method 1: Using Outlook

Here, make sure you have an updated version of Outlook Classic on your system.

Phase 1- Configure Office 365 account

Firstly, open Outlook and go to File > Info > Add Account.
Enter Office 365 email address and click on Connect.
After that, follow the steps Outlook is asking to verify your account.
Once done, wait for the sync process to complete.

Phase 2: Import EML Files to Outlook 365

Now, create a new folder in the Office 365 mailbox.
Go to the location where EML files are saved.
Simply right-click > choose Open with > Outlook.
Then, on the top you will see an option say Move.
Click and select > Other folders. Choose the folder newly created in Office 365.
Now, click on OK to import EML file to Microsoft 365.

Limitations:

Using this approach, users need to import each EML file one-by-one which means they need to repeat the process every time.
The folder structure will not be maintained.
It is not an ideal method for organization users who deal with large collections of data.
There is a high risk of losing emails as users can get confused while importing single files.

Method 2: Upload EML to Office 365 via Thunderbird

This method also has 2 phases that should be followed properly to avoid any error during EML to Office 365 migration process.

Phase1- Add Microsoft 365 account

Open Thunderbird.
Go to its Menu > New Account > Email. Enter full name and the email address.
Next, choose IMAP from the options and verify the account.
Don’t rush, wait for Thunderbird to completely sync your Office 365 mailbox.

Phase2- Migrate EML to Office 365

Now, navigate to Menu > Add-ons and Themes.
Search ImportExportTools NG and click on Add to Thunderbird option.
After that, right-click on the folder where you want to access EML files.
Select ImportExportTools NG > Import EML Messages > All messages from a directory and subdirectories.
Select your EML files and click on Import.

This is how you can import EML to Microsoft 365 successfully in batch.

Limitations:

Transferring all folders at once can slow down Thunderbird and may lead to system lag during the process.
It totally depends upon Thunderbird and its add-on setup.
Requires a stable internet connection throughout the import process.
This approach does not guarantee folder structure accuracy as it may get affected.

EML files generally contain attachments and they can have something important, crucial and confidential data which needs to be preserved and kept intact for several uses. The question is, does the manual techniques mentioned preserve all the attachments in a way the user expects? Or do they even care about your attachments or not. Let’s move forward to the next EML to Office 365 migration tool to see if it can be useful or not.

Expert-Verified EML to Office 365 Migration Tool for Direct Import

To simplify the process and avoid manual methods drawbacks, many professionals recommend the RecoveryTools EML Converter as a smart choice. This tool supports a user-friendly interface with multiple advanced features that enables both technical and non-technical users to import EML files hassle-free to Microsoft 365 in a few clicks.

Moreover, the certified software provides a free trial version that allows users to import a limited number of emails before purchasing the license key. Also, it enables them to test tool features and functionality as a complete evaluation. So, download it now.

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EML to Office 365 Migration Using Expert Software – Working Steps

Download, install, and run the software as per the instructions.
Select the option to upload your EML files or folders.
Check all the required data files as per your needs for selective conversion.
Now, choose Office 365 from the select saving option list to import EML to Office 365.
Enter Office 365 email address in the specific field.
Click on Next to start the process. Once done, you will be notified.

Why EML to Office 365 Migration Tool Wins Over Manual Method? Key Features

This best EML to Office 365 converter supports multiple filters like date range, subject, or sender to allow users to selectively import data.
Supports both single file selection and bulk folder upload that provides a flexible data importing feature.
The tool guarantees to preserve email headers such as To, From, CC, BCC, subject, and timestamps accurately throughout the import process.
Easily imports EML files created from platforms like Mozilla Thunderbird, Windows Live Mail, and others without showing any error.
This comprehensive tool generates a complete log report after the migration is complete. It helps users track the entire process to be aware of any failure.
Works smoothly on all modern and old Windows OS versions.
It supports secure login with Microsoft 365 using updated authentication protocols.
The tool has the ability to import large-sized EML files with attachments without slowing down the system performance.

Clear Comparison Between Manual and Automated Approach

Feature	Manual Methods	Pro Method
Ease of Use	Requires technical knowledge and involves complex steps.	Support simple-to-operate interface with direct steps for both expert and home users.
Batch Import	Support limited imports and not efficient for large-scale businesses.	Support bulk mode to import thousands of EML files at once with safety and saving time.
Standalone Utility	No, requires Thunderbird or Outlook email client installation.	Yes, this is a standalone software and does not require any other third-party application.
Advanced Filters	No, users need to manually select and transfer EML files.	The tool has multiple advanced filters for selective import.
Security	Limited security; Depends on the client and network.	High-level security with secure account authentication.
Technical Support	No support is available	24/7 technical support
Cost	Free but consume resources	Paid with free trial version. Plans are pocket-friendly for all users.

Popular Asked Questions

Q1. Can I directly upload EML files to Outlook Web App?

No, you cannot. The Outlook Web App does not provide any direct EML upload feature. However, you can use the professional tool to directly import EML files to Microsoft 365 accounts.

Q2. Will attachments remain intact after migration?

Yes, the certified EML to Office 365 tool guarantees users that all the attachments and email properties are preserved intact throughout and even after the migration process.

Q3. Can I import multiple EML files at once?

Yes, while the manual methods support limited upload. But you can use the automated tool as it supports bulk importing thousands of EML files at once without altering any data.

Q4. Can I import EML files without Outlook installed?

Yes, try the above mentioned professional tool. It works independently and does not require Outlook installation for the EML to Microsoft 365 migration.

Q5. What is the fastest method to import EML to Office 365?

Honestly, the best and fastest way to migrate EML files is the EML to Office 365 migration tool. It will transfer even large data in few minutes whereas the manual methods may slow down system speed.

Conclusion

In the end, I would conclude that if your goal is to enjoy a secure, accurate and fast migration then choose the professional method. It is highly recommended as it will help you batch import EML to Office 365 without losing a bit of information and in a structured way. Whereas manual methods are also there and work fully but they are unreliable for bulk migrations and only suitable for users who have a few EML files to import. So, decide and rely on the best EML to Office 365 converter based on your needs.

Read Next: Expert Guide to Import EML Files to Gmail