Email archives outlive the clients that created them. A Gmail Takeout export lives on as a 12 GB MBOX file you cannot open anywhere except Thunderbird. An Apple Mail export sits on an old hard drive in a format that Outlook refuses to read. Migrate from one email client to another, archive a project mailbox for legal hold, hand off a mailbox to your accountant for tax review — in every case, the format mismatch between MBOX and EML stops you.
Email Converter is a Mac and iPhone app that converts between MBOX and EML in both directions. Drag a file in, choose the target format, export. The conversion happens entirely on your device — no upload, no cloud account, no third-party access to your correspondence. It is a one-time purchase, available on both platforms with the same license.
How to Use Email Converter
On macOS, the workflow is drag-and-drop. Open Email Converter, drag your MBOX file onto the app window, and the app reads it and shows the message count. Choose your output format (EML or MBOX), select an output folder, and click Convert. The app writes the converted files to your chosen folder and shows progress in a bar that handles multi-gigabyte mailboxes without freezing the UI.
On iPhone and iPad, the workflow is via the Files app. Tap the plus button in Email Converter, browse to your MBOX file in Files (iCloud Drive, Dropbox, or local storage all work), choose the output format, and export. The converted files save back to Files, where you can share them via AirDrop, attach to an email, or open in another app.
Batch conversion is supported. Drag multiple MBOX files onto the Mac window at once — the app processes them sequentially with a single output folder. On iPhone, batch processing is one file at a time but the per-file conversion is fast enough that it does not matter for typical archive sizes.
Output options control how EML files are organised. You can write each message as an individual .eml file (one file per email), or you can consolidate multiple EMLs back into a single MBOX for easier transfer. The EML files preserve all message headers, body content (HTML and plain text), and attachments — nothing is lost in the conversion.
Source compatibility covers the major exports: Gmail Takeout downloads (MBOX), Thunderbird mailbox exports (MBOX), Apple Mail mailbox exports (the .mbox folder structure, which Email Converter treats as a directory of MBOX files), and Outlook PST archives that have been converted to MBOX via a third-party intermediate step.
The privacy model is on-device only. No file is uploaded to any server. The app contains no analytics, no ads, no telemetry. Your correspondence stays between you and the app.
How to Migrate Emails Between Clients
The most common reason to convert email formats is a migration between clients. The pattern depends on the direction.
Gmail to Apple Mail. Download your Gmail data from Google Takeout. Takeout exports your mailbox as one or more MBOX files, depending on size. Open Email Converter, drag the MBOX in, convert to EML. Drag the resulting EML files into an Apple Mail mailbox folder — Apple Mail imports them directly. For folder structure preservation, create the target Apple Mail folder hierarchy first, then drop the EML files into the matching folders.
Thunderbird to Apple Mail. In Thunderbird, right-click a folder, choose "Export Folder", and save as MBOX. In Email Converter, convert to EML. Drag the EML files into Apple Mail. The same pattern works for any folder — convert each Thunderbird folder you want to migrate.
Apple Mail to Thunderbird. In Apple Mail, select a mailbox and use Mailbox → Export Mailbox. This produces a .mbox folder (which is technically a directory containing an mbox file). In Email Converter, point at this folder, convert to individual EML files, then import into Thunderbird via the ImportExportTools add-on.
Archiving for the long term. EML is the most portable format because every email client can read individual .eml files. Convert any mailbox you want to keep long-term from MBOX to EML, label the resulting folder with the year and source (e.g., "client-correspondence-2020-gmail"), and store it in cold storage. Twenty years from now, when MBOX may be obscure, EML will still be readable in whatever email client exists by then.
Large mailboxes. If your MBOX is larger than 5 GB, split it first using Mbox Splitter Pro into smaller chunks (1–2 GB each), then convert each chunk separately. This is faster, uses less memory, and lets you parallelise the conversion across multiple sessions if you are migrating a very large archive.
How Email Converter Compares to Other Tools
The main competitors are paid desktop applications (Mac and Windows only) and web-based converters that require uploading your email to a third-party server.
| Tool | Mac | iPhone | Batch | On-device | Free |
|---|---|---|---|---|---|
| Email Converter | Yes | Yes | Yes | Yes | One-time |
| Aid4Mail | Yes | No | Yes | Yes | Paid ($50+) |
| MailConverter online | No | No (web) | Limited | No (upload) | Freemium |
| Manual drag in Thunderbird | Yes | No | No | Yes | Free |
The two reasons to choose Email Converter over the alternatives: it runs on iPhone (none of the others do), and it does not upload anything to the cloud (web-based converters all do, which is a serious problem if your emails contain confidential information). The one-time purchase pricing also beats subscription tools at the typical use case — you convert a few archives and never need the tool again, but you keep the ability to convert future archives forever.
Frequently Asked Questions
What is the difference between MBOX and EML format?
MBOX is a single file containing multiple emails concatenated together — it is the standard export format for Gmail, Thunderbird, and Apple Mail. EML is a single file per email — it is the format used by Outlook, Windows Mail, and most email archiving tools. Converting MBOX to EML splits the mailbox into individual message files. Converting EML to MBOX consolidates many individual files into one container. Both formats preserve full message content (headers, body, attachments).
Does Email Converter upload my emails to a server?
No. Email Converter processes all files locally on your device. Your emails never leave your Mac or iPhone. The app makes no network calls related to conversion — it only contacts Apple servers for receipt validation when you first install. After install, it operates completely offline.
Can Email Converter handle large MBOX files?
Email Converter handles most MBOX files efficiently — the app streams the file rather than loading it all into memory, so a 5 GB mailbox uses only modest RAM during conversion. For very large mailboxes (over 5 to 10 GB), we recommend splitting the file first using Mbox Splitter Pro, then converting each part separately. This makes the conversion faster and lets you parallelise.
Which email clients use MBOX format?
Gmail (via Google Takeout), Mozilla Thunderbird, Apple Mail, The Bat!, and Evolution all export to MBOX. Microsoft Outlook uses PST format, which requires a separate conversion step (e.g., via Aid4Mail or Outlook's own export-to-MBOX option) before Email Converter can process it. Once the PST is in MBOX format, Email Converter handles the EML conversion normally.
Download Email Converter
Email Converter is available on the Mac App Store and the iOS App Store as a one-time purchase. The same license activates on both platforms via your Apple ID.
