Microsoft Outlook is the email and calendar program that comes in six versions. Learn how classic and new Outlook differ, where your mail sits and which versions Microsoft still supports.
Microsoft Outlook is Microsoft's email, calendar, contacts and tasks program. Six different apps use the name, from classic Outlook for Windows to the mobile apps.
Your account type decides where mail sits. Microsoft 365, Exchange and IMAP accounts keep mail on a server and cache it in an OST file. POP accounts store mail in a PST file.
Classic Outlook has a File tab and new Outlook has a Settings gear. Versions 2016, 2019 and 2021 are past support. Version 2024 stays supported to October 2029.
Microsoft Outlook is Microsoft's program for email, calendars, contacts and tasks. You read mail, book meetings and store names in one window.
Search for help and the first problem shows up fast. Six different apps share the name and the steps for one rarely match the screen of another.
Microsoft released the first version in January 1997 with Office 97. That release replaced the older Exchange client and Schedule+. The name stayed while the apps behind it changed many times.
One program can hold one mailbox or several. A work account on Exchange sits beside a personal Outlook.com address and an IMAP account. All of them show in one folder list.
The program is a client and not a mail service or a server. Outlook.com is a service and Exchange Server is a server. The client shows your mail while the service or server stores it.
The desktop program came first. Microsoft later added a web version for organizations and a free mailbox on Outlook.com. Phone apps followed after the Acompli purchase in 2014.
Microsoft announced a preview of the new Windows app in 2022. Support for the old Windows Mail and Calendar apps ended in 2024 when the new app took over.
Microsoft's email and calendar client comes as six different apps. Every one keeps your data in its own way.
.pst and .ost on WindowsSeen the name on an old PC? Outlook Express is a separate program from the 1990s. Section 9 explains the difference.
Outlook is a family of six apps. Match the row to where you open it and you know which one you use.
Six apps carry the name today. Two install on Windows. One opens in a browser for work or school accounts and one serves personal accounts. The last two cover the Mac and your phone.
Windows has two. Classic Outlook is the long established desktop app. It comes with Microsoft 365 apps or with Office 2021 and 2024.
New Outlook is the newer desktop app that Microsoft built to replace it. A toggle moves you between the two. Section 3 compares them and section 4 shows how to tell them apart.
The web version serves work or school accounts. Microsoft calls it the browser version used by organizations. You sign in at outlook.office.com with the account that your employer or school gave you.
Outlook.com is the free personal mailbox. Microsoft says it replaced Hotmail and Hotmail addresses still work. The Microsoft comparison of account types explains why personal and work accounts behave differently.
The Mac app is free for personal use according to Microsoft. It carries a Legacy Outlook switch that separates the old and new versions. Entourage came before it and Microsoft Entourage covers that older Mac client.
The mobile apps cover iOS and Android. Microsoft calls them free on both. Microsoft bought the Acompli app in December 2014 and renamed it Outlook in January 2015.
Mac mail sits in its own set of files. OLK files covers what those files hold.
| You want | Use this version | Why |
|---|---|---|
| A free Windows app | New app | Microsoft says it is free to use |
| Full PST and public folder support | Classic app | Microsoft advises classic for public folders |
| Mail in any browser | Web version or Outlook.com | Nothing to install |
| Mail on a phone | Mobile app | Free on iOS and Android according to Microsoft |
| Mail on a Mac | Mac app | Free for personal use |
Your account decides some of these choices. Work accounts follow the rules of the organization that issued them.
Classic Outlook has the File tab and opens PST files directly. New Outlook has the Settings gear and costs nothing. A toggle moves you between them.
Microsoft built the new Outlook for Windows to replace the classic desktop app. Microsoft says the new app brings newer features, assisted tools and a simpler design. The Microsoft guide to the new Outlook for Windows walks through the switch.
Both apps open your mail. They differ in menus, file support and cost. The table shows the gaps that matter on a normal workday.
| Feature | Classic | New |
|---|---|---|
| Where to look | File tab at the top left | Settings gear at the top right |
| Switching | Toggle labeled Try the new Outlook | Toggle off opens classic |
| Public folders | Microsoft advises classic if you depend on them | Limited support |
| PST files | Opens them in the app | Needs an account with a Microsoft 365 subscription |
| Cost | Microsoft 365 apps or a perpetual Office license | Free to use |
| Default status | Stays with Office apps | Default on new Windows 11 PCs |
Microsoft states that the new app is free to use and the default mail app on new Windows 11 PCs. See the Microsoft notice on Windows Mail and Calendar for the wording.
Microsoft plans the move in three stages called opt in and opt out and cutover. In the first stage the new app is off by default and you try it with a toggle. In the second stage it is on by default.
At cutover users cannot switch back to classic. The Microsoft migration stages page gives no calendar dates for stages two and three. It promises managed Enterprise plans at least 12 months of notice.
Microsoft also says existing classic installs under perpetual and subscription licensing stay supported until at least 2029. Section 7 lists the dates for every version.
The Microsoft migration page covers the desktop apps for Windows. It does not cover the Windows Mail and Calendar apps.
Keep the classic app if public folders matter to you or if you open PST files in the program. Microsoft gives that advice for public folders in its own guide.
Microsoft says a missing toggle means your account is not supported yet or your administrator blocked the new app. Ask your administrator before you search for a fix.
Try the new app if you want the free option on Windows. You can switch the toggle off and return to classic at any time.
Check the top left for a File tab and the top right for a Settings gear. The File tab means classic Outlook and the gear means new Outlook.
Microsoft gives one quick test for Windows. If the Settings button is missing then you use classic Outlook. The Microsoft page on which Outlook you have covers every platform.
File > Office Account. If you do not see Office Account then select Help. The version and build sit under Product Information.Settings > General > About Outlook. The version shows on the right.File > About Outlook.
Help articles for the classic app name the File tab in step one. Articles for the new app name the Settings gear. Match the tab or gear in the article to your screen before you follow any steps.
On the web, work or school accounts sign in at outlook.office365.com or through microsoft365.com. Personal Hotmail addresses use Outlook.com. The Microsoft sign in page for Outlook on the web lists the links.
On a Mac, Microsoft ties the old and new apps to a Legacy Outlook switch. You switch it off to try the new one. The Help menu then holds a Revert to Legacy Outlook command.
Accounts you add in one Mac version do not appear in the other. Read the Microsoft page on Outlook for Mac before you switch.
Not by itself. Outlook 2016 and 2019 both report version 16. Read the full Product Information box on the Office Account page and not just the first number.
No. Microsoft says the Mail app in Windows 10 and 11 is a different program. Microsoft ended support for the Windows Mail, Calendar and People apps on 31 December 2024.
Windows Mail covers the older client that followed Outlook Express. Section 9 compares the two.
The master copy sits on a server for most accounts. A POP account is the exception because the PST file can hold the only copy.
Your mail sits in one of two places. The master copy lives on a server for most accounts. Windows adds a local file that holds either a cache or the only copy.
Microsoft says a PST file holds messages plus contacts, appointments, tasks, notes and journal entries. The Microsoft page on Outlook Data Files also states that some accounts use "an offline Outlook Data File (.ost)" instead.
An OST file is "a synchronized copy of the messages saved on a server" in Microsoft's words. The server keeps the master copy.
Sync works both ways. A message you delete in the program also disappears from the server copy.
A PST file is a container you own. POP accounts fill one and you can create more for archives or exports. Read PST files and OST files for sizes and repair.
Microsoft says PST files go to the Documents\Outlook Files folder by default. OST files sit in C:\Users\<username>\AppData\Local\Microsoft\Outlook on Windows 10 and 11. AppData is hidden.
To see the real path in the classic app select File then Account Settings and then Data Files. Select Open File Location. Close the program before you copy anything.
Yes with one condition. The account in the new app must have a Microsoft 365 subscription. Then you select Settings and Files and Outlook Data Files and Add file. The Microsoft overview of PST files in new Outlook lists the steps.
Microsoft's client saves a single message as an MSG file by default. Calendar events travel as ICS files. Mac mail has its own files covered under OLK files.
Servers keep mailboxes in a database of their own. EDB files explain the format that Exchange uses and Exchange Server explains the server.
Microsoft 365, Exchange, Outlook.com, IMAP and POP accounts all work. The type decides which local file Windows builds.
Five kinds of account work with Outlook. Work accounts use Microsoft 365 or Exchange. Personal accounts use Outlook.com. IMAP and POP cover most other providers.
| Account type | Master copy sits | Local file | What it means for you |
|---|---|---|---|
| Microsoft 365 or Exchange | Server mailbox | OST | The server holds your master copy |
| Outlook.com and Hotmail | Microsoft servers | OST | Works across web, mobile and desktop apps |
| IMAP | Mail server | OST in Outlook 2016 and later | Folders stay in step with the server |
| POP | Your PC after download | PST | The PST can hold the only copy |
IMAP keeps mail on the server and syncs folders. POP downloads mail to your PC. Microsoft says POP accounts store their information in Outlook Data Files.
Outlook 2013 and earlier wrote IMAP mail into a PST. Version 2016 and later use an OST for IMAP accounts. Our PST files guide explains how that change affects old profiles.
POP suits one device. IMAP and Exchange and Outlook.com suit several because the server copy reaches every device you sign in on.
Version 2013 and later connect to Outlook.com natively through Exchange ActiveSync. Older versions needed the Hotmail Connector add in.
Both give you a server mailbox. Your employer decides whether that mailbox sits in Microsoft's cloud or on its own Exchange Server.
Microsoft lists work or school accounts on Microsoft 365 or Exchange Online plus Microsoft accounts like Outlook.com. It also lists Google, iCloud, Yahoo, POP and IMAP accounts. The Microsoft page on Outlook for Mac gives the build numbers that every one needs.
A Microsoft account is personal. You use it for Outlook.com and other consumer services. A work or school account comes from an organization and signs in only to the services that organization set up.
That split matters when the program asks you to sign in. Choose the wrong type and the mailbox you want never appears. The Microsoft comparison of account types spells out the difference.
Companies that host their own mail use Exchange Server. Others use Lotus Notes, Zimbra or MDaemon.
Outlook 2016, 2019 and 2021 are out of support. Outlook 2024 stays supported to October 2029 and classic installs stay supported until at least 2029.
Outlook 2016 and 2019 reached end of support on 14 October 2025. The Microsoft 2025 end of support list names both along with Office 2016 and 2019. Outlook 2021 followed in October 2026.
| Version | Status | Date from Microsoft |
|---|---|---|
| 2016 and 2019 | Ended | 14 Oct 2025 |
| 2021 | Retired under the Modern policy | 13 Oct 2026 |
| LTSC 2021 | Ended | 13 Oct 2026 |
| 2024 | Supported | Retirement on 10 Oct 2029 |
| Office LTSC 2024 | Supported | End of support on 10 Oct 2029 |
| Classic installs | Supported | At least 2029 |
Microsoft lists Outlook 2021 on the Microsoft 2026 end of support list. The Microsoft lifecycle page for Outlook 2021 and the Microsoft lifecycle page for Outlook 2024 hold the product dates. The Microsoft lifecycle page for Office LTSC 2024 matches the 2029 date.
Microsoft lists the start of Outlook 2021 on 5 October 2021 and Outlook 2024 on 1 October 2024. Office LTSC 2024 started on 18 September 2024.
Microsoft lists Outlook 2021 as a retirement under its Modern policy. It lists Outlook LTSC 2021 as end of support under its Fixed policy. The date and the result are the same for you.
Version 2024 gives you the longest fixed date at October 2029. Classic installs share the 2029 floor that Microsoft states. Managed Enterprise plans get at least 12 months of notice before a stage changes.
Microsoft stops new security updates and other updates. It also ends free and paid assisted support and online technical content. Your copy still exists but no one patches it.
Microsoft says support for legacy Outlook for Mac ends in October 2026 and depends on your license. See the Microsoft page on Outlook for Mac for details.
Move to a version that Microsoft still supports. Your choices are Outlook 2024 or a Microsoft 365 plan with desktop apps or the free new app. Copy your data files first.
The classic app has no announced end date. Microsoft says it supports existing installs until at least 2029 and gives managed plans 12 months of notice before later stages.
The new app, Outlook.com, the mobile apps and the Mac app for personal use are free. The classic app needs Microsoft 365 apps or a perpetual license.
Four versions cost nothing according to Microsoft. Those are the new app, Outlook.com, the mobile apps and the Mac app for personal use. The classic app is the paid one.
| Version | Cost | Catch |
|---|---|---|
| New app for Windows | Free to use | PST support needs an account with a Microsoft 365 subscription |
| Outlook.com | Free with 15 GB of mailbox storage | Ads show in the inbox with an ad label |
| Mac app | Free for personal use | Legacy support depends on your license |
| Mobile apps | Free on iOS and Android | None listed |
| Classic app | Comes with Microsoft 365 apps or Office editions | Needs a paid license |
Microsoft sells Microsoft 365 Basic as the ad free option. The plan lists 100 GB of mailbox storage. Check the Microsoft Outlook plans page for current wording.
Not for the new one. Microsoft says it is free to use and also states that Outlook is included for free with Windows.
The classic app is different. Microsoft ships it with Microsoft 365 subscriptions and with perpetual releases like Outlook 2021 and Outlook 2024.
Work or school accounts sign in with an account that an organization assigns. Your employer or school decides the cost. Personal accounts use Outlook.com and cost nothing.
Free does not mean the same features everywhere. The new app asks for a Microsoft 365 subscription before it adds PST support. Read the catch column before you choose.
A free Outlook.com account has 15 GB of mailbox storage and core security features like spam filters. Free accounts without a subscription also see marked ads in the inbox.
Microsoft adds that Hotmail and Live and MSN accounts work across all the apps with free or paid plan benefits. Your old address needs no change.
Work and school mailboxes follow the plan your organization buys. Your administrator sets the size and the features.
Outlook Express, Windows Mail, Windows Live Mail and Thunderbird are different programs. None of them is an older name for Outlook.
This old mail client is a separate program. Microsoft shipped it with Internet Explorer 4 and bundled it with Windows 98 through Windows Server 2003. Windows Vista replaced it with Windows Mail.
It started as Internet Mail and News in 1996. Outlook arrived in 1997 as part of Office. The two shared a word and nothing else. Outlook Express tells that story in full.
| Program | Maker | Period | What to know |
|---|---|---|---|
| Outlook Express | Microsoft | Windows 98 to Windows XP era | Stores mail in DBX files from version 5 on |
| Windows Mail | Microsoft | Started with Windows Vista | Replaced Outlook Express |
| Windows Live Mail | Microsoft | Part of Windows Essentials | Free desktop client |
| Windows Mail and Calendar apps | Microsoft | Ended 31 Dec 2024 | Replaced by the new app |
| Mozilla Thunderbird | Mozilla | Current | Stores mail in MBOX files |
Version 6.0 shipped with Windows XP in October 2001. It was the last release with that branding and version 7 never shipped.
Windows Mail took over in Windows Vista. Windows Live Mail came later as a free client in the Windows Essentials suite. Windows Mail covers the Vista client.
Microsoft ended the Windows Mail, Calendar and People apps on 31 December 2024 and points users to the new app. That change retired the Mail app in Windows 10 and 11.
Old forum posts use one word for both programs. Check the date of a post and the Windows version it names. Posts about the old client name Windows 98 through XP.
Mozilla Thunderbird is a free desktop client. Microsoft's client ties to Exchange and Microsoft 365. Thunderbird stores mail in MBOX files while Microsoft's client uses PST and OST.
Moving mail between the two means converting files. PST files and MBOX files show how both formats work. Apple Mail is the Mac native option beside both.
Most faults trace to one data file or one account or one server. Find which of the three you have and go to its page.
Most faults trace back to a data file or an account or a server. Match your symptom to the right page.
Your account type points to the file. Exchange and IMAP and Outlook.com accounts cache mail in an OST and POP accounts store mail in a PST. The page for that file holds the repair steps.
Fix the cause and not the symptom. A message about a data file points to a PST or OST. A message about a sign in points to the account. A message about a mailbox database points to the server.
The Windows error guides cover Windows error codes and not Outlook faults. If your problem needs a page we do not have yet then Send us the file details and we will look.
Outlook is an app and not a file format. PST and OST hold your mail on Windows while MSG, EML and ICS carry single items.
Outlook has no single file format. Storage uses PST and OST while single items use MSG, EML and ICS.
| Format | What it holds | Notes |
|---|---|---|
.pst | Messages, contacts, appointments, tasks, notes and journal entries | Personal Storage Table. Open proprietary format |
.ost | Synchronized copy of server mail | Used by Exchange, IMAP and Outlook.com accounts |
.msg | One message or item | Default when you save or forward an email |
.eml | One message in plain text | Standard format that clients like Thunderbird read |
.ics | Calendar events | Partial iCalendar support |
winmail.dat | TNEF wrapper for attachments | Many other clients cannot read it |
| Version | Internal number | Released |
|---|---|---|
| 97 | 8.0 | 1997 |
| 98 | 8.5 | 1998 |
| 2000 | 9.0 | 1999 |
| 2002 | 10 | 2001 |
| 2003 | 11 | 2003 |
| 2007 | 12 | 2007 |
| 2010 | 14 | 2010 |
| 2013 | 15 | 2013 |
| 2016 | 16 | 2015 |
| 2019 | 16 | 2018 |
Version 2003 added a junk mail filter and blocked automatic image loading. Version 2007 switched to the Word rendering engine. Versions 2016 and 2019 both report number 16.
Contacts move as vCard files. Outlook supports vCard 2.1 but not several contacts in one vCard file.
PST stands for Personal Storage Table. EML and MSG both hold one message. ICS holds calendar events. TNEF is the wrapper behind winmail.dat.
These names make more sense with what a file format is beside them. The file format guides lists the rest.
Check the top corners. Section 4 shows the File tab and Settings gear test.
Check the account type. Section 6 maps every account to its local file.
Does a PST or OST file refuse to open? PST files and OST files cover size limits and repair. EDB files cover the server side.
Is your mail on a Microsoft server? Exchange Server explains the server and EDB files explain the database it keeps.
Did you find an old program called Outlook Express? Outlook Express and Windows Live Mail cover the clients that came before the modern apps.
Do you want to compare other clients? Mozilla Thunderbird and Apple Mail are two. Lotus Notes and IncrediMail are two more.
Do you need to move calendar entries or Mac mail? ICS files carry events between programs. OLK files cover the Mac app. Extension basics sit in what a file format is.
Are your contacts in a .vcf file? The VCF file guide covers vCard versions and how Outlook imports one card at a time.
Is the fault in Windows instead? Windows error guides start from the exact error text. The FileFix category index groups every guide by topic. Start again from the FileFix home page if you landed here by mistake. Send us the file details if your problem needs more than this page explains.