Reviewed by Shubham Dixit, Independent Expert in Email Forensics and Data File Conversion. Shubham is an external reviewer and not a PCDOTS employee.
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Switching from the Postbox desktop client to an Office 365 account? The reason is usually the same one Postbox users keep running into, your mail is trapped on one computer and you want it in the cloud where you can reach it anywhere. The move is very doable, and there is a useful fact about Postbox that gives you two honest ways to do it.
Summary Postbox stores mail in MBOX, so you can migrate to Office 365 two ways. Free route, export your Postbox folders to MBOX, add both accounts to a mail client and drag the mail up over IMAP. Direct route, load the Postbox profile into PCDOTS Postbox Converter and upload straight to Office 365 with folders intact.
The one fact that makes this simple?
Here is what most guides never mention. Postbox is built on the same Mozilla foundation as Thunderbird, which means it stores your mail in the MBOX format inside a profile folder on your computer. That single fact is what gives you options.
Because your Postbox mail is sitting in standard MBOX files, you are not locked into one magic tool. You can move it the free way using other software that understands MBOX, or the direct way with a converter that uploads it to Office 365 in one go. Office 365 itself has no Import Postbox button, so both routes work around that the same way, by treating your mail as the portable MBOX data it already is.
The free route: export and IMAP upload
If you have time and only one mailbox, you can do this without paying. It uses MBOX as a bridge and a desktop client to push the mail up.
- In Postbox, export the folders you want. Postbox can save folders out, and being Mozilla based, its profile MBOX files can also be read by Thunderbird.
- Install Thunderbird and import those MBOX files using the free ImportExportTools NG add on.
- Add your Office 365 account to Thunderbird over IMAP, which supports modern sign in.
- Drag the imported folders onto the Office 365 account and let Thunderbird upload them.
- Check the folders appear in Outlook on the web.
It works, and it costs nothing. The honest trade offs are the usual ones for a manual IMAP move. It is fiddly, you are setting up a second client as a middleman, large folders can upload slowly, and it handles one mailbox at a time. For a single account and a patient afternoon, it is a fair choice.
The direct route: straight to Office 365
For a cleaner path, or more than one mailbox, the PCDOTS Postbox Converter reads your Postbox profile directly and uploads it into Office 365 in one run, no Thunderbird middleman. It is the same engine as the wider Email Converter, focused on Postbox.
Step 1: Load the Postbox profile
Open the tool, click Open, choose Postbox from the account list and point it at your Postbox profile data.
Step 1: Loading the Postbox profile data.
Step 2: Preview and select the mail
Your Postbox folders load with a full message preview. Confirm the data reads correctly and untick anything you do not want in the cloud.
Step 2: Previewing the Postbox mail.
Step 3: Choose Office 365 and sign in
Click Export, select Office 365 from the providers, enter the destination account login and start. The upload runs with progress on screen.
Step 3: Selecting Office 365 from the export options.
When it completes, open Outlook on the web and your Postbox folders are there in the Office 365 mailbox. Prefer a local copy instead of the cloud? Choose PST, PDF or MBOX at the export step rather than Office 365.
“With any MBOX based client, the thing to verify after upload is nested folders. A flat inbox always moves cleanly, but deep subfolder trees are where a rushed migration flattens the structure. Open the Office 365 mailbox and confirm the hierarchy matches Postbox before you assume the job is finished. The messages are rarely the problem, the shape sometimes is.”
Shubham Dixit · Independent Expert, Email Forensics and Data File Conversion
Which route should you take?
Both get your mail into Office 365. The choice comes down to time, mailbox count and how much fiddling you can tolerate.
| Your situation | Better route |
|---|---|
| One mailbox, time to spare, want it free | Export and IMAP upload |
| Several mailboxes or large data | Direct converter upload |
| You also want a local PST or PDF copy | Direct converter upload |
| You would rather not set up a second client | Direct converter upload |
After the migration
Whichever route you used, spend two minutes confirming the move before you stop using Postbox.
- Compare folder counts between Postbox and Office 365, nested folders included.
- Open a few older messages and check the original dates survived.
- Open a message with an attachment and confirm it downloads.
- Keep your Postbox profile, or an exported MBOX copy, as a backup until you are sure.
People also ask
Can I move Postbox emails to Office 365 for free?
Yes, for one mailbox with patience. Export the Postbox folders to MBOX, import them into Thunderbird, add your Office 365 account over IMAP and drag the folders up. It is free but fiddly and handles one account at a time.
Where does Postbox store its emails?
Postbox is built on the Mozilla platform, like Thunderbird, so it stores mail in MBOX files inside a profile folder on your computer. Those standard files are what both migration routes work from.
Does Office 365 have a built in Postbox import?
No. Office 365 cannot read a Postbox profile directly, so you either bridge the mail through a client over IMAP or use a converter that uploads the Postbox data into the Office 365 mailbox for you.
Will my folder structure and attachments be kept?
Yes, with both routes when done carefully. The direct converter recreates the folder tree automatically, while the IMAP method preserves it if you drag folders across in order. Attachments stay attached either way.
Do I need Postbox installed to use the converter?
The converter reads the Postbox profile data, so as long as you can point it at that profile folder, you do not need Postbox actively running. A copied profile from another machine works too.
Moving on from Postbox
The thing worth remembering is that your Postbox mail was never really locked in. It has been sitting in standard MBOX files the whole time, which is why you get a free route and a direct one instead of a single take it or leave it tool. Choose the free IMAP bridge if you have one mailbox and an afternoon, or the converter if you want several mailboxes, a local backup, or simply less fuss.
Once your folders are verified in Office 365, you can keep the Postbox profile as an archive and enjoy reaching your mail from any device.
