Written by Jennifer Walsh. Reviewed for technical accuracy by Shubham Dixit, Independent Expert in Email Forensics and Data File Conversion.
Shubham is an independent external reviewer and not an employee of PCDOTS.
Quick answer. You cannot import an MBOX through the iCloud webmail site, it has no import button. iCloud Mail is IMAP, so you import the MBOX into a mail client connected to your iCloud account, Apple Mail on a Mac or Thunderbird anywhere, and it syncs up to iCloud and shows in the webmail. A tool can upload it over IMAP too.
On this page
Why the iCloud website has no import?
If you have been hunting for an import button on the iCloud website, you can stop, there is not one. The iCloud Mail webmail lets you read and send, but it has no way to upload a mailbox file. So an MBOX cannot go in that way, and that is the sticking point most people hit.
The way in is IMAP. iCloud Mail is an IMAP service, so you point a mail client at your iCloud account, bring the MBOX into that client, and move it into an iCloud folder. Because it is IMAP, whatever you place there syncs up to iCloud, and moments later the same mail appears in the iCloud webmail and on every Apple device signed in. The MBOX never touches the website, it rides in through a client.
The website has no way in. A client syncs the MBOX up, and then it is in the webmail.
“People burn a lot of time looking for an upload button in iCloud webmail that has never existed. iCloud Mail is plain IMAP, so the trick is simply to put the mail into a client that is signed in to iCloud and let the sync carry it up. The one snag that catches everyone is the password, iCloud will not accept your normal one from a third party client, you have to generate an app-specific password first. Do that and Thunderbird or any tool connects straight away.” Shubham Dixit, Email Migration reviewer (draft, pending approval)
The easy way on a Mac, Apple Mail
iCloud is Apple’s own service, so on a Mac this is the shortest path, and it is free. Your iCloud account is almost certainly already set up in Apple Mail.
Import the MBOX. In Apple Mail choose File, Import Mailboxes, pick Files in mbox format, and select your MBOX. It lands in an Import folder under On My Mac.
Move it into iCloud. In the sidebar, drag the imported messages or mailbox into a folder under your iCloud account. That drag is the step that matters, because iCloud is IMAP, the mail uploads to iCloud as you drop it, and within a while it appears in the iCloud webmail and on your other Apple devices.
Anywhere else, Thunderbird
On Windows, Linux, or a Mac without Apple Mail set up, free Thunderbird does the same job. The important part, which some guides leave out, is that importing the MBOX into Thunderbird is only half of it, you then have to move it into the iCloud folder.
Add iCloud to Thunderbird. Set up your iCloud account as an IMAP account in Thunderbird, using an app-specific password, see the next section.
Import the MBOX. Install the free ImportExportTools NG add-on, right click a local folder, choose ImportExportTools NG, then Import mbox file, and select your MBOX.
Drag it into iCloud. Now drag those imported messages from the local folder into a folder under your iCloud account in Thunderbird. This is what actually sends them to iCloud, they sync up and land in the webmail.
The app-specific password
This is the detail that quietly blocks people. Because iCloud uses two-factor authentication, it will not accept your normal Apple password from Thunderbird, a converter, or any third-party client. You need an app-specific password.
Sign in at appleid.apple.com, go to the sign-in and security section, choose App-Specific Passwords, generate one, and use that as the password when you add iCloud to Thunderbird or the tool. Apple Mail on a Mac already signed in to iCloud does not need this, only outside clients do.
Same result either way. The only real difference is the password step.
The bulk way, a tool
The client routes are fine for a mailbox or two. When you have many MBOX files or very large ones and would rather not import and drag by hand, a converter uploads them to iCloud over IMAP directly. The PCDOTS MBOX Converter loads MBOX files or a whole folder and sends them straight into your iCloud account over IMAP, in bulk. Two honest notes, it runs on Windows, so a Mac user is usually better off with Apple Mail, and it needs the same app-specific password any outside client does. A free version uploads the first ten items per folder so you can test it first.
The tool route, for many or very large MBOX files.
Here are the steps with the screens.
Step 1. Install and run the converter on Windows, then open the menu.
Step 2. Choose Email Data Files, MBOX, and add your files or folder.
Step 3. Open the Export menu and select IMAP.
Step 4. Enter your iCloud address and app-specific password, then Save to upload.
For the client routes in more depth, see our guides to import MBOX to Apple Mail and import MBOX to Thunderbird, and you can open a file first with a free MBOX file viewer.
The methods compared
Match the route to your device and how many files you have.
| Method | Best for | Good to know |
|---|---|---|
| Apple Mail | Mac users, free | Easiest, no app password needed |
| Thunderbird | Windows or Linux, free | Needs an app-specific password |
| MBOX Converter tool | Many or very large files | Windows, uploads over IMAP |
Frequently asked questions
Can I import an MBOX in the iCloud webmail?
No. The iCloud website has no import feature. You import the MBOX into a mail client connected to your iCloud account over IMAP, and it syncs up so it appears in the webmail.
How do I import MBOX to iCloud for free?
On a Mac, use Apple Mail, import the MBOX and drag it into your iCloud mailbox. On other systems, use Thunderbird with an app-specific password, import the MBOX and drag it into the iCloud folder.
Why will Thunderbird not accept my iCloud password?
iCloud uses two-factor authentication, so third-party clients need an app-specific password. Generate one at appleid.apple.com and use that instead of your normal Apple password.
Why did importing the MBOX not put it in iCloud?
Importing into a local folder is only half the job. You then have to drag those messages into a folder under your iCloud account, which is what uploads them to iCloud.
Will a large MBOX fit in iCloud?
iCloud’s free tier is 5 GB shared across your account, so a very large mailbox may exceed it. Check your available storage, or upgrade to iCloud+, before a big import.
Can I upload many MBOX files at once?
Yes. A converter can send a batch of MBOX files to iCloud over IMAP in one pass, which is easier than importing and dragging each one by hand.
Once it is in iCloud, it is everywhere
The thing to remember is that the website was never the way in. You bring the MBOX into a client that is signed in to iCloud, Apple Mail on a Mac or Thunderbird elsewhere, drag it into the iCloud folder, and the sync does the rest. And once those messages are in iCloud, they are not stuck in one place, they show up in the iCloud webmail and on your iPhone, iPad and Mac, wherever you are signed in. So do it once through a client, and your old mailbox follows you across every Apple device you own.
