How to Import eM Client to Thunderbird

There’s no direct ‘Import from eM Client’ button in Thunderbird. The two clients use different native formats, so an intermediate step is required depending on where your mail is stored. This guide covers every working method. Free methods first; use paid tools only when the free options fall short.

Tips : Don’t touch anything in eM Client until you’ve confirmed Thunderbird received the data correctly. Keep the source intact throughout.

What Can Actually Be Migrated?

Email is the straightforward part. Contacts and calendars need separate steps.

Data	Transfers	How
Emails	Yes	EML, MBOX, or IMAP
Attachments	Yes	Embedded in EML/MBOX files
Folder structure	Partial	IMAP preserves automatically; file-based methods need manual folder setup in Thunderbird
Sent Items/Drafts	Yes	Treat them as folders same process as Inbox
Contacts	Separately	Export as vCard (.vcf) from eM Client, import into Thunderbird address book
Calendars	Separately	Export as .ics from eM Client, import into Thunderbird Calendar
Account settings	No	Configure accounts fresh in Thunderbird

Contacts and calendars are separate operations. This guide covers email migration only.

Method 1: IMAP Synchronisation

IMAP syncing is probably the handiest way to get an email stash from an online email provider’s server. The good news is it works with pretty much any service that’s got IMAP going – you’re talking Gmail, Outlook.com and Yahoo here. Now, when you’ve got your emails all stored up online, Thunderbird can connect up to your old server and the new one, and just sync all the mail data back and forth.

Tip : Check first: In the EM Client’s left panel, look at where your folders sit. If they’re listed under your email address (e.g., yourname@gmail.com), that’s server-stored mail. If they’re under ‘Local Folders,‘ skip to Method 2.

Steps

1. First, fire up Thunderbird. Then, File, New, and Existing Mail Account\.
2. Just fill in the easy stuff, name, email address and password.
3. Thunderbird detects your server settings automatically in most cases.
4. When prompted, choose IMAP not POP3.
5. Click Done. Thunderbird syncs your folders from the server.

Folder hierarchy, sent mail, drafts. All preserved because the server manages the structure.

Watch for these

• First sync is gonna take some time, especially if you’re talking to big accounts ( 10,000+ emails or something). Thunderbird does a sort-of-intelligent loading process, downloading headers first, then the actual mail. Just leave it be and let it run.
• Local-only folders won’t appear via IMAP. Anything under EM Client’s ‘Local Folders’ needs the EML method below.
• Duplicate risk: If you later also import EML files for the same folder, you will get duplicates. Use one method per folder.

Method 2: EML Files (Free Works for Local Mail)

eM Client can save emails as individual .eml files. Thunderbird imports them through a free add-on. This is the standard manual path for local mail.

Part A: Export from eM Client

1. Pick the folder you want to move ( start with your Inbox, probably )\.
2. Press Ctrl+A ( Windows ) or Cmd+A ( Mac ) to select everything.
3. Right-click, Save As, and choose a destination folder on your disk.
4. eM Client saves one .eml file per message.
5. Repeat for each folder: Sent, Drafts, any custom folders.

Tip : Mirror your eM Client folder structure on disk before you start. Create /Export/Inbox/,/Export/Sent/,/Export/Work/, whatever matches your layout. You will need this organisation during import.

Part B: Install ImportExportTools NG in Thunderbird

Thunderbird doesn’t import EML natively. You need the ImportExportTools NG add-on (free):

1. Thunderbird, Tools, and then Add-ons and Themes.
2. Search “ImportExportTools NG”.
3. Install and restart Thunderbird.

Part C: Import into Thunderbird

1. In Thunderbird, create a folder matching the eM Client folder you are importing (right-click Local Folders and New Folder).
2. Right-click that folder and ImportExportTools NG, Import messages, Import EML files from a directory (and subdirectories).
3. Navigate to your exported folder and confirm.
4. Repeat per folder.

The Real Limitation  A 3,000 email folder becomes 3000 individual .eml files when you export it out – and importing 10 folders means you’re looking at 10 separate tasks to get that done. This works fine up to a few hundred emails. Beyond that, it gets slow and repetitive which is where Method 4 helps.

Method 3: Importing MBOX Files If You Already Have Them

Thunderbird stores emails as MBOX files internally, so if you’ve got MBOX files from a Google Takeout export, a server backup or a previous migration you can import them right away.

Tip : eM Client however doesn’t support MBOX exports natively. If your source is eM Client, your path is: export EML, convert to MBOX, and import. Method 4 handles that conversion.

Importing an existing MBOX file

1. Firstly, install ImportExportTools NG (same as Method 2).
2. Right-click Local Folders (or any account) in Thunderbird.
3. ImportExportTools NG and Import mbox file.
4. Select your .mbox file and confirm.

One MBOX file = one folder. Ten folders = ten imports. For MBOX files above 2-3 GB, the import is slow but completes do not interrupt it.

Method 4: MacSonik EML Converter (For Large Local Mailboxes)

The manual EML approach breaks at scale. If you have thousands of emails across 20 folders, exporting and importing each one manually takes a full day. And still produces errors you do not catch until a week later. The MacSonik EML Converter helps with that. It takes a folder of EML files exported from eM Client and converts them to MBOX in one go. One operation covers all folders. You then import those MBOX files into Thunderbird.

The Workflow

1. Firstly, export EML files from eM Client (Method 2, Part A).
2. Open MacSonik EML Converter and add your EML folder.
3. Select MBOX as the output format.
4. Use the date range filter if you only need specific periods.
5. Enable duplicate removal if your eM Client had sync overlap.
6. Run conversion and get one MBOX file per folder.
7. Import MBOX files into Thunderbird (Method 3).

What’s Preserved?

Email body, attachments, sender/recipient metadata, dates

Folder separation; one MBOX per folder

Attachments embedded in the output files

Free Trial The free version processes 50 emails per folder; enough to verify output quality before committing to the full migration.

Product: macsonik.com/eml-converter/

Explore How MacSonik Works in Detail

Method 5: MacSonik MBOX Converter (For Processing MBOX Files Before Import)

Once you have MBOX files from Method 4, a Google Takeout export, or a server backup, you can import them directly into Thunderbird. But raw MBOX files sometimes need work first.

When Does This Apply?

Converted MBOX files contain duplicates from sync overlap between eM Client and your server	You want to filter by date before importing (e.g., only the last two years)
MBOX files are oversized and need splitting before import	You are working with Google Takeout MBOX exports, which can be messy

The MacSonik MBOX Converter handles batch processing across multiple MBOX files, with built-in duplicate removal, a date range filter, and no file size cap. You can keep the output in MBOX format which Thunderbird can read, or you can swap it out for EML, PST, PDF or CSV if you need to change formats at a later stage.

Tip :If your MBOX files are all good to go and in good order you can probably just skip this step and get straight into importing them into Thunderbird (Method 3). This step exists for when they are not.

Product: macsonik.com/mbox/converter/

Explore How MacSonik Works in Detail

Method 6: MacSonik IMAP Backup Tool (For IMAP Account Switches)

Method 1 covers accessing the same IMAP account in Thunderbird. But sometimes you are not just switching clients you are switching accounts.

Scenarios Where This Matters

Moving from a work IMAP account to a personal one	Archiving an old IMAP mailbox before the account is deleted
Migrating email from one server to a different one	If you’re on the verge of giving up on eM Client, maybe it’s time to pull a full local copy of your live IMAP account.

MacSonik IMAP Backup Tool connects directly to your IMAP server, downloads your mailbox, and exports to MBOX, EML, PST, or other formats. It also handles IMAP-to-IMAP migration, moving mail between accounts without downloading everything locally first.

If you are keeping the same email account and just switching from eM Client to Thunderbird, Method 1 is faster and free. This tool is for moving, archiving, or converting IMAP mailbox data.

Product: macsonik.com/imap-email-backup/

Explore How MacSonik Works in Detail

Which Method Fits Your Situation?

Your situation	Use this
Mail is on Gmail, Outlook.com, or any IMAP server	Method 1. add the account directly in Thunderbird
Local eM Client folders, under a few hundred emails	Method 2. EML export + ImportExportTools NG
Local eM Client folders, large mailbox (1,000+ emails)	Method 4. MacSonik EML Converter, MBOX, Thunderbird
You already have clean MBOX files	Method 3. direct MBOX import
MBOX files need deduplication, filtering, or splitting	Method 5. MacSonik MBOX Converter
Switching IMAP accounts, not just email clients	Method 6. MacSonik IMAP Backup Tool
Mix of server mail and local folders	IMAP for server mail + EML/Method 4 for local folders

Troubleshooting

Emails missing after import   Check whether the EML export actually completed. A folder that had 800 messages in eM Client would logically have 800 .eml files on disk. But if the numbers dont add up, just try re-exporting that folder	Attachments missing   EML files embed attachments if the export completed correctly, they are in the file. Double-click a .eml file directly in Windows Explorer or Finder to verify. If the attachment opens there, the import should carry it through.
Folders not organised correctly   The EML import method does not reconstruct your folder hierarchy automatically. Create matching folders in Thunderbird first, then import into each one separately. Mass-importing into a single folder loses all structure.	Duplicate emails   This tends to happen when you try to bring Method 1 and Method 2 together for the same folder we’ve got IMAP sync pulling from the server and EML import pulling from local files, both trying to do their thing at the same time. Pick one source per folder. The MacSonik EML Converter duplicate removal option cleans up if you already ran both.
Thunderbird frozen during import   Normal for large files. MBOX files over 1-2 GB make Thunderbird unresponsive during import. Do not close it. Import by folder rather than everything at once.	IMAP sync not showing all folders   In Thunderbird, right-click your account and Subscribe and make sure all folders are checked. Some IMAP providers do not auto-subscribe new clients to every folder.

Contacts and Calendars (Quick Reference)

Contacts   In eM Client, go to File -> Export and choose the option for vCard (.vcf) – its pretty straightforward. And in Thunderbird, you can get to it by going to your Address Book and then picking Tools -> Import and then picking out your .vcf file.

Calendars   In the eM client, right click on a calendar and you should see an option to export it as a .ics file. Then over in Thunderbird, head on into Calendar -> Events and Tasks and you’ll find the option to import the .ics file you just saved.

Frequently Asked Questions

 

Verification Checklist

Before uninstalling eM Client or deleting anything:

• Message count matches per folder (check three or four folders, not just Inbox).
• Open messages from different years confirm body text and attachments.
• Send Items present and readable.
• Drafts folder populated if you had drafts.
• Search in Thunderbird returns results for a known subject line.
• Sender names and dates display correctly.
• The subfolder structure matches what you had in eM Client.

Tips : If something is off, fix the gap and re-verify before clearing the source data from eM Client.

Sources

• Thunderbird ImportExportTools NG: 
• Mozilla Thunderbird support: 
• MacSonik EML Converter:
• MacSonik MBOX Converter: 
• MacSonik IMAP Backup Tool:
• eM Client documentation: 

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