Corbett

Office 365 Backup Tool

Corbett Office 365 Backup Tool exports a Microsoft 365 mailbox to a local disk as PST, MBOX, EML, MSG, PDF, HTML, CSV or TXT. Sign-in happens on Microsoft's own page, with MFA where the account uses it. Folder tree, attachments and timestamps come along. Windows only.

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4.6 out of 5 from 683 reviews

Mailbox data downloads to the local PC. Nothing goes to a Corbett server.

Free demo, scanned clean on VirusTotal and a 30-day money-back window.

Lifetime licence from $99 Free trial saves 10 emails per folder

Microsoft 365 specifics

Office 365 Backup Tool for Mail, Contacts and Calendar

A removed licence deletes the mailbox 30 days later. Corbett's Office 365 backup tool copies one Exchange Online mailbox at a time over the same connection Outlook uses and saves an offline copy. The lists below show what arrives and what stays behind.

Comes across

All mail folders
Attachments
Inline images
Message dates
Read/unread status
Full headers
Contacts
Calendar

Folders backed up

Inbox
Sent Items
Drafts
Archive folder
Deleted Items
Junk Email
Custom folders

Saves as

PST
MBOX
EML
MSG
PDF
HTML
CSV
TXT
vCard
ICS

Not included

Online Archive
Shared mailboxes
Public folders
OneDrive
SharePoint
Teams chats
Mailbox rules
Account settings

The Archive folder and the Online Archive are two different things

The Archive folder sits inside the mailbox and is backed up like any other folder. The Online Archive is a second mailbox that Microsoft attaches to some plans. It is not reachable like the main mailbox, so it stays on the server.

Office 365 mailbox to PST

Core features

Office 365 Backup Tool Features in Five Screens

Five screens of the Microsoft 365 backup tool, from sign-in to the saved file.

Adding a Microsoft 365 account in Office 365 Backup Tool

Connect

Microsoft 365 Sign-In With MFA

Select Office 365 from the list and server details fill in on their own. A Microsoft sign-in window opens for the address and password. Approve the two-step prompt if the account has one and the mailbox loads. The credential stays on Microsoft's side.

Host and port detected automatically
Two-step verification, also called MFA, works as normal
No admin rights needed to back up a personal work mailbox
No app password to generate, Microsoft 365 mail has no app password route
Several mailboxes queued in one run, every one with its own sign-in

Folder selection

Select Office 365 Folders to Back Up

The mailbox opens as a folder tree with a checkbox on every branch and a message count beside it. A single project folder can be saved on its own. Deleted Items and Junk Email drop out with one click apiece.

A checkbox on every folder and subfolder
Message counts shown before the run
Subfolder structure kept in the output
Empty folders hidden with the compact view

Message preview

Preview Office 365 Emails Before Export

Every message opens in a preview pane with four analysis views beside it. IT staff copying a mailbox for a legal request use the header and raw views to confirm what they share.

Content opens body, sender, recipients and subject
Message header maps the servers the mail passed through
Properties sums up size, priority and file names
Hex and raw message print the untouched MIME source

Selective backup

Back Up a Leaver Mailbox by Date or Sender

Filters are applied before the run starts. Everything a departing employee exchanged with one client in one financial year is saved on its own, which is the shape most Microsoft 365 backup requests take.

Date range filter with From and To dates
Sender, recipient, subject or message content
Only messages that carry an attachment
Message size, to leave large mail out
Skip junk or duplicate messages

Output options

Save Office 365 Mail to Disk or Mailbox

Select the destination at the end: a local folder, an external drive, a mapped network share or straight into a second live account. Document output follows a naming rule, so a folder of thousands of files stays ordered and searchable.

Mail formats: PST for Outlook, MBOX for Thunderbird or Apple Mail, EML, MSG
Document formats: PDF, HTML, CSV, TXT
Direct transfer into Google Workspace, another Microsoft 365 account or any IMAP host with the email migration tool
PST output opens in any Outlook edition and imports back into Microsoft 365
Attachments, email addresses and phone numbers extracted on their own
Every run is a full copy of the ticked folders. There is no scheduler, so a repeat backup starts by hand

To restore a saved PST into a mailbox later, use the email recovery software, the restore half of the same download.

Before connecting

Microsoft 365 Login Through Entra ID

Microsoft changed the rules for third party software in 2022 and many guides were never updated. Three points to settle before adding a mailbox.

Changed

A password alone no longer works

Microsoft switched off password based sign-in for mail software in October 2022. Any program with its own Microsoft 365 password form is refused. Corbett's Office 365 backup tool opens Microsoft's sign-in window instead and receives a token, not the password. Microsoft brands the method modern authentication.

Not needed

There is no app password

Gmail and Yahoo issue app passwords for outside programs. Microsoft 365 business mail never offered that route, so any guide that says to create one is about another provider. Authenticator, SMS codes and FIDO2 security keys all show up in the normal Microsoft prompt.

One admin sign-in does not cover the tenant

It works mailbox by mailbox. Every account is added with its own sign-in, then all of them run together. An administrator who needs every mailbox in the organization without every user present should use Content Search in Microsoft Purview, covered below.

A login window that shuts with an error usually means the user is blocked from signing in, or a Conditional Access policy in Entra ID limits which apps may connect. Both settings belong to the tenant admin, not to the backup tool.

Free demo

Test the Office 365 Backup Tool on One Mailbox

Install the free demo, sign in on Microsoft's page, tick a folder and select a format. Nothing reaches the disk until the run starts.

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Why a copy

Microsoft 365 Mail Retention and Backup Limits

Microsoft keeps the service running. Keeping the data falls on the customer, and that split is written into its shared responsibility model. A copy on a disk that is not connected to the account also stays untouched if ransomware or a compromised sign-in empties the mailbox. These are the windows that matter.

14 days

A message removed from Deleted Items

It moves to the Recoverable Items folder and stays there for 14 days by default. An administrator can raise that to 30 days at most. After that it is gone unless a retention policy or hold was already in place.

30 days

A mailbox whose licence is removed

When a user leaves and the licence is taken away, Exchange Online holds the mailbox for 30 days. Then it is deleted and no administrator or support ticket can bring it back. Most requests for an Office 365 backup tool start with that 30 day limit.

Paid add-on

Microsoft 365 Backup restores, it does not export

Microsoft's own backup service costs $0.15 per GB per month and restores mail back into Microsoft 365. It does not produce a file on a local disk. A local PST or PDF on a company-controlled disk is a different thing, and that is what a Microsoft 365 backup tool such as Corbett writes.

Mailbox size is capped by plan, 50 GB on Business plans and 100 GB on E3 and E5. A full mailbox rejects new mail. Moving old years to a local file is the usual way to keep the account under the cap.

Before purchase

Outlook Export vs Office 365 Backup Tool

If Outlook is already installed, it can export a mailbox to PST at no cost. That handles a single account in a single format. The table marks where it runs out.

Task	Outlook export	Office 365 Backup Tool
Cost	Free with Outlook	$99 one time
One mailbox, once, to PST	Built for exactly that	Handles it too, but the price covers the rows below
Which Outlook	Classic Outlook. New Outlook exports mail only	Outlook not needed at all
Output format	PST only	Eight formats including PDF and MBOX
Date, sender or subject filter	Not in the export wizard	Applied before the run
Several mailboxes	One account per export, one export at a time	Queued together in one run
Waiting on a sync first	Yes, the entire mailbox must download into Outlook	No, it pulls from the server directly
Headers and raw source	Not shown during export	Full preview before the run

Rows tinted green are the ones where Outlook wins.

One account, PST only and classic Outlook already installed: use Outlook and skip the purchase. Administrators who need many mailboxes without every user present have Content Search in Microsoft Purview, which needs the eDiscovery Manager role and produces export packages that expire after 14 days. Both routes are covered in Office 365 mailbox to PST.

Specifications

What the Office 365 Backup Tool Runs On

Download details

Released: Dec 2020
Download size: 87.4 MB
Trial limit: 10 emails per folder
Delivery: Download link and key by email
Licence: Lifetime, up to 5 machines

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System

Hard disk: 150 MB to install, plus room for output
RAM: 4 GB minimum
Processor: 1 GHz, 2.4 GHz advised
Rights: Run as Administrator
Outlook: Not required

Supported editions

Runs on Windows 11 through 7, either 32 or 64 bit. Windows Server editions from 2008 through 2025.

No macOS or Linux build.

Corbett has built Windows email utilities since 2020. Support tickets go to the same engineers who build the Microsoft 365 backup tool.

Working process

Office 365 Backup Tool Video Guide

Prefer screenshots? The IMAP backup guide walks through the same Office 365 backup step by step.

Common questions

Office 365 Backup Tool Questions

Signing in, what is copied and where the backup tool stops.

Does Microsoft not back up Microsoft 365 already?

Microsoft keeps the service available. It does not keep a copy of your mail for you, and its shared responsibility model says so. A deleted message is held for 14 days by default, a mailbox with no licence for 30 days. After those windows the data is gone. A file on your own disk is the only copy nothing else controls.

Why does Office 365 Backup Tool open a Microsoft sign-in window?

Microsoft retired Basic Authentication for Exchange Online in October 2022, so typed passwords no longer reach a mailbox. The tool opens Microsoft's sign-in page, the user authenticates there and Exchange Online returns an OAuth token. The program never sees the password.

Does Office 365 Backup Tool work with two-step verification?

Yes. Because sign-in runs on Microsoft's page, any authenticator, text code or security key shows up just as it does in a browser. Nothing has to be turned off and no app password is involved, since Microsoft 365 mail has no app password route.

Can an admin back up every Microsoft 365 mailbox at once?

No. One mailbox is added per sign-in. Several can be queued and run together, but every one needs its own sign-in. For the entire organization without every user present, Content Search in Microsoft Purview is the route and it needs the eDiscovery Manager role.

Does the Microsoft 365 backup include the Online Archive?

No. The Online Archive is a separate mailbox that Microsoft attaches to certain plans and it is not exposed like the main mailbox. The Archive folder inside the mailbox is different and is backed up like any other folder.

Can a Microsoft 365 shared mailbox be backed up?

A shared mailbox has no sign-in of its own, so it cannot be added directly. If the administrator has assigned it a licence and enabled sign-in, it behaves like a user mailbox and can be added. Otherwise Content Search is the route for shared mailboxes.

PST or PDF for a Microsoft 365 mailbox backup?

Choose PST when the mail may go back into Outlook or another Microsoft 365 account later. Choose PDF when the copy is for someone without Outlook or for a legal or HR file that must open in ten years. Many people write both, since the run can be repeated with a different format.

Does the backup include Microsoft 365 contacts and calendar?

Yes, when the mailbox carries them. Contacts export to a vCard file and calendar items to an ICS file beside the saved mail. Teams chats, OneDrive files and SharePoint libraries are separate services and stay where they are.

Does a backup free space in the Microsoft 365 mailbox?

Not by itself. The backup is one way only, so the server copy stays exactly as it was. Once you have opened the local copy and checked it, delete the old folders in Outlook yourself to bring the account back under its 50 GB or 100 GB cap.

Is there a Microsoft 365 mailbox size limit?

No. The licensed edition puts no cap on mailbox size or message count. A large mailbox takes longer because Exchange Online limits download speed, but nothing stops before the end. A dropped link does not restart the run; the export carries on with the next unsaved item.

Can the Microsoft 365 mailbox of an employee who has left be backed up?

Yes, as long as the mailbox still exists and someone can sign in to it. Do it before the licence is removed or within 30 days of removal. After that the mailbox is deleted and there is nothing left to copy.

Does Microsoft 365 mail pass through Corbett's servers?

No. It runs on your PC and connects from there to Microsoft. The output lands on the disk or drive you select. Corbett stores nothing and relays nothing.

Does Office 365 Backup Tool run on Mac or Linux?

No. Office 365 Backup Tool needs Windows: any desktop release from 7 up, or Windows Server 2008 onward. Mac and Linux builds do not exist.

Can I trial the Office 365 tool for free?

Yes. The trial signs in to any Microsoft 365 tenant mailbox, loads all folders and unlocks preview and every filter. It exports the first 10 emails per folder, letting real tenant mail prove the output before purchase.

Step by step

Office 365 Backup Guides for Common Tasks

Every guide below covers one task around an Office 365 backup tool run, from the first click to the saved file.

Exporting Microsoft 365 mail

Switching tenants

Working with the PST

Other providers are covered on the email backup software page. To move a Microsoft 365 account into another account, use the email migration tool. To convert a finished file, use the email converter tool. To open a saved file without exporting anything, use the free email viewer software. Apple Mail users have the iCloud backup tool, Google Workspace domains the Google Workspace backup tool and shared hosting mail the Webmail backup tool. More walkthroughs: Migrate Office 365 account to another account, Save Outlook 365 emails to hard drive and Migrate Outlook emails to Office 365. Sibling pages: Gmail backup tool, Outlook.com backup tool, Hotmail backup tool and Yahoo backup tool.

User testimonials

Office 365 Backup Reviews from Admins

Office 365 Backup Tool runs on the Corbett wizard rated by 683 business and home users.

4.6 out of 5

Collected across 683 reviews from software directories and direct customer feedback. The three examples below are verbatim.

Saved O365 mailboxes locally

Awesome tool. I bought Office 365 backup wizard full version to save my O365 mailboxes locally for future use. The software has performed really well, and saved all data without any error.

Samantha Roth

Microsoft 365 mail to IMAP

I wanted to move my Office 365 mails to my IMAP account. After looking on the internet for a while, I came upon this tool and, it really helped me to achieve the archive process.

Steven Frew

Office 365 backup to hard drive

My Manager asked me to secure all mails to hard drive. But manual backup is very time-taking process. So, I decided to go with Office 365 email backup tool which helped me to download the emails easily.

Dave Adams

Get started

Back Up Office 365 Mail Before the Licence Goes

Install the Office 365 Backup Tool trial, sign in on Microsoft's page and export a handful of messages per folder. Personal licence costs $99 one time, with a 30-day money-back window.

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87.4 MB · Windows 11 to 7 and Windows Server 2025 to 2008 · 30 day money back