How to Import MBOX to Yahoo Mail

Leena Taylor Paul
Updated: May 8, 2026 • Import • 6 Min Read

Summary: Import MBOX to Yahoo Mail with one of two reliable methods.

Open the MBOX file in Mozilla Thunderbird with the ImportExportTools NG add-on. Then drag the messages from Local Folders into your Yahoo IMAP account.
Use a dedicated MBOX to Yahoo converter that connects directly over IMAP and uploads every message in one job.
Yahoo server: imap.mail.yahoo.com, port 993, SSL. An App Password is required.

Why Import MBOX to Yahoo Mail?

MBOX is a plain-text mailbox format used by Thunderbird, Apple Mail, Postbox, Eudora, and many Unix mail clients. The file lives on your computer, not in any web mailbox.

As a result, you cannot read it from the Yahoo web interface. To search the messages alongside your Yahoo inbox, you have to upload them over IMAP.

Common reasons include leaving a Thunderbird or Apple Mail profile and wanting the mail server-side. In addition, you may have inherited an MBOX export from a colleague, or you may be consolidating multiple archives before another provider switch.

Yahoo Mail’s IMAP support makes the upload straightforward. However, you must first generate an App Password.

What You Need Before You Start

The MBOX file or files you want to import (extension .mbox or no extension at all).
A Yahoo Mail account with two-step verification enabled.
An App Password generated at login.yahoo.com/account/security. Yahoo blocks regular passwords for third-party IMAP clients.
A stable internet connection. Yahoo throttles bulk IMAP uploads on flaky links.

Tip: Generate the App Password once. Copy it to a password manager. Then reuse it everywhere you connect to Yahoo over IMAP.

Yahoo Mail IMAP Server Settings

Both methods below use the same connection details. Therefore, configure them once and reuse:

Incoming (IMAP): imap.mail.yahoo.com, port 993, SSL/TLS
Outgoing (SMTP): smtp.mail.yahoo.com, port 465 (SSL) or 587 (STARTTLS)
Username: your full Yahoo address (e.g. name@yahoo.com)
Password: the 16-character App Password from Yahoo Account Security

Method 1: Import MBOX to Yahoo with Thunderbird (Free)

Thunderbird is free, cross-platform, and supports MBOX natively. With one add-on, it can read any MBOX file you have on disk.

Steps to Import MBOX into Yahoo

First, install Thunderbird and open it.
Next, open the menu and go to Add-ons and Themes. Search for ImportExportTools NG, and install it. Restart Thunderbird when prompted.
Then right-click Local Folders in the left pane. Choose ImportExportTools NG > Import mbox file, then pick Import directly one or more mbox files. Select your MBOX file(s) and confirm. The folder appears under Local Folders with all your messages.
Add your Yahoo account: Account Settings > Account Actions > Add Mail Account. Enter your name, full Yahoo address, and your App Password. Click Configure manually and use the IMAP settings above. Click Done.
Once Yahoo’s folders appear in the left pane, drag the imported folder from Local Folders into the Yahoo account (Inbox or a custom subfolder). Thunderbird uploads the messages over IMAP.
Finally, when the upload finishes, log into Yahoo Mail in your browser. Confirm the messages and attachments appear in the chosen folder.

Tip: Yahoo Mail throttles IMAP uploads. Therefore, if you are moving thousands of messages, split the drag into batches of 500 to 1,000 at a time to avoid timeouts.

Method 2: Use a Dedicated MBOX to Yahoo Converter

A dedicated converter is the simpler route in three cases. First, you may not want to install Thunderbird. Next, you may have many MBOX files to combine. Finally, you may need to preserve unusual headers and attachments exactly.

EmailBakup MBOX Converter reads MBOX, EML, EMLX, and PST sources. Also, it uploads directly to Yahoo, Gmail, Outlook.com, Microsoft 365, or any IMAP host.

Steps with the MBOX to Yahoo Converter

First, download and install EmailBakup for Windows or macOS.
Next, click Add Files or Add Folder. Then choose MBOX as the source format.
Browse to the folder containing your MBOX file(s) and click Select Folder. The tool scans the folder and loads every MBOX it finds.
Once messages are loaded in the left pane, you can preview any item. As a result, you can confirm attachments and formatting look correct.
Then click Export. In the destination dropdown, choose IMAP.
Enter your Yahoo email and App Password. Also enter the IMAP server imap.mail.yahoo.com on port 993 with SSL.
Pick a target folder in Yahoo (Inbox or a custom subfolder), then click Start.
The converter authenticates with Yahoo and starts uploading. Watch the progress on screen. When it finishes, you see a confirmation.
Finally, log into Yahoo Mail in your browser to verify the imported folder appears with the correct count and attachments.

Related Reading:

Which Method Should You Choose?

Already have Thunderbird and only one or two MBOX files: use Method 1 (drag and drop).
Many MBOX files to combine: use Method 2 (dedicated converter).
Want the upload to run unattended: Method 2 is the better fit.
Prefer zero extra software: stick with Method 1 if Thunderbird is already installed.

Common Errors and Fixes

Authentication failed for imap.mail.yahoo.com

This almost always means you used your regular Yahoo password. Therefore, generate a new App Password at Yahoo Account Security and paste the 16-character string into your client.

ImportExportTools NG menu does not appear

First, confirm the add-on is enabled in Add-ons and Themes. Next, restart Thunderbird. The Local Folders right-click menu only shows the entries after a clean restart.

Upload stalls or times out on large batches

Yahoo limits IMAP request rates. As a result, you should split large folders into batches of 500 to 1,000. Also, run the import overnight if your archive is many gigabytes.

Folders show fewer messages than the source MBOX

This usually means the upload stopped mid-batch. Therefore, compare counts and re-drag the missing range, or rerun the converter on the same source folder. Yahoo deduplicates by Message-ID, so reruns will not create duplicates.

Frequently Asked Questions

What is the Yahoo Mail IMAP server?

The incoming IMAP server is imap.mail.yahoo.com on port 993 with SSL/TLS. The outgoing SMTP server is smtp.mail.yahoo.com on port 465 (SSL) or 587 (STARTTLS).

Do I need an App Password?

Yes. Yahoo blocks third-party clients from using your regular password. Therefore, you must enable two-step verification and generate a 16-character App Password.

Will MBOX attachments and folder structure survive the import?

Yes. Attachments, headers, sender, date, and subject are preserved. Folder structure is preserved if you create matching folders in Yahoo before dragging, or if the converter recreates them automatically.

Is there a size limit?

Yahoo Mail accepts messages up to 25 MB each over IMAP. Total mailbox storage on a free Yahoo account is 1 TB. As a result, the only practical limit is upload speed and Yahoo’s per-session throttling.

Can I import multiple MBOX files at once?

With Thunderbird, you can import several MBOX files into Local Folders and drag them across in sequence. In contrast, the dedicated converter can scan an entire folder of MBOX files and upload them in a single job.