I have windows 11, Microsoft 365 Classic Outlook. I want to change from the .ost inbox file to the ,pst data file.

Question

I have windows 11, Microsoft 365 Classic Outlook. I want to change from the .ost inbox file to the ,pst data file.

Steve Martin Sr 20

I have windows 11, Microsoft 365 Classic Outlook. I want to change from the .ost inbox data file to my ,pst data file.

Steve Martin Sr 20 Reputation points

2026-08-23T21:06:35.4833333+00:00

More information. I deleted the OST file and started over to connect via POP to year’s old existing PST inbox data file. Classic outlook, Microsoft 365, windows 11. Connection successful to yahoo.com. But still incoming emails are not downloading. How to fix?
Hornblower409 14,815 Reputation points

2026-08-24T03:20:40.1533333+00:00

@Steve Martin Sr said

Connection successful to yahoo.com. But still incoming emails are not downloading

Just to be sure, please check that your setup looks like mine. I am using two POP GMail accounts, but Yahoo should look similar.

File -> Account Settings -> Account Setting.

Send/Receive -> Send/Receive Groups -> Define Send/Receive Groups

Settings for group "All Accounts"

Select "All Accounts' and [Edit]

Select an account on the left. Account settings should look like:

Then do a Send/Receive All and Show Progress. Any errors?
Steve Martin Sr 20 Reputation points

2026-08-24T15:15:00.41+00:00

All those settings above look good, but in my Send/Receive All and Show Progress, it is stuck in processing and no downloads are happening.

Could it be I need to contact AT&T and Yahoo to fix some setting?

History: After a decade of service, I switched iphones from AT&T to Verizon in January and in May the downloading stopped. I contacted AT&T and had them re-activate the account for the Yahoo.com to download. In my Outlook Classic, I deleted and reinstalled the email account selecting .imap, which created a new .ost inbox data file. I now had 2 inbox files in my Outlook and to get the incoming mails over to the existing .pst File , I made a rule in Outlook to copy the incoming emails from the .ost to the .pst inbox folder. This worked, but is confusing. So in Outlook, I deleted and reinstalled my email account, selecting POP (pop.mail.yahoo.com). But the downloads are now stuck saying in processing. Nothing is happening.

What needs to be done?
Hornblower409 14,815 Reputation points

2026-08-24T18:29:37.2533333+00:00

@Steve Martin Sr said

contacted AT&T and had them re-activate the account for the Yahoo.com ... selecting POP (pop.mail.yahoo.com). But the downloads are now stuck

You can get the correct Yahoo POP settings by doing a search for: POP access settings and instructions for Yahoo Mail

But those may not be the right ones for an AT&T account (email ends with att.net) that is just hosted on Yahoo. For those do a search for Get AT&T email server settings

Note that in both cases you have to use a generated App Password:

For AT&T: Search for AT&T Create a secure mail key

For Yahoo: Search for Yahoo Generate and manage 3rd-party app passwords

Answer accepted by question author

Hornblower409 14,815

@Steve Martin Sr said

I want to change from the .ost inbox data file to my ,pst data file

Are you using POP email accounts and in your old Outlook setup you had all of your POP Inboxes using a single PST?
If so, see [External Non-Microsoft Site] https://www.slipstick.com/outlook/email/deliver-pop3-accounts-one-outlook-inbox/

If not, please give me some more details on what your old Outlook setup was and what you are trying to do with the new setup.

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1 additional answer

Your answer

Steve Martin Sr 20 Reputation points

2026-08-23T21:06:35.4833333+00:00

More information. I deleted the OST file and started over to connect via POP to year’s old existing PST inbox data file. Classic outlook, Microsoft 365, windows 11. Connection successful to yahoo.com. But still incoming emails are not downloading. How to fix?
Hornblower409 14,815 Reputation points

2026-08-24T03:20:40.1533333+00:00

@Steve Martin Sr said

Connection successful to yahoo.com. But still incoming emails are not downloading

Just to be sure, please check that your setup looks like mine. I am using two POP GMail accounts, but Yahoo should look similar.

File -> Account Settings -> Account Setting.

Send/Receive -> Send/Receive Groups -> Define Send/Receive Groups

Settings for group "All Accounts"

Select "All Accounts' and [Edit]

Select an account on the left. Account settings should look like:

Then do a Send/Receive All and Show Progress. Any errors?
Steve Martin Sr 20 Reputation points

2026-08-24T15:15:00.41+00:00

All those settings above look good, but in my Send/Receive All and Show Progress, it is stuck in processing and no downloads are happening.

Could it be I need to contact AT&T and Yahoo to fix some setting?

History: After a decade of service, I switched iphones from AT&T to Verizon in January and in May the downloading stopped. I contacted AT&T and had them re-activate the account for the Yahoo.com to download. In my Outlook Classic, I deleted and reinstalled the email account selecting .imap, which created a new .ost inbox data file. I now had 2 inbox files in my Outlook and to get the incoming mails over to the existing .pst File , I made a rule in Outlook to copy the incoming emails from the .ost to the .pst inbox folder. This worked, but is confusing. So in Outlook, I deleted and reinstalled my email account, selecting POP (pop.mail.yahoo.com). But the downloads are now stuck saying in processing. Nothing is happening.

What needs to be done?
Hornblower409 14,815 Reputation points

2026-08-24T18:29:37.2533333+00:00

@Steve Martin Sr said

contacted AT&T and had them re-activate the account for the Yahoo.com ... selecting POP (pop.mail.yahoo.com). But the downloads are now stuck

You can get the correct Yahoo POP settings by doing a search for: POP access settings and instructions for Yahoo Mail

But those may not be the right ones for an AT&T account (email ends with att.net) that is just hosted on Yahoo. For those do a search for Get AT&T email server settings

Note that in both cases you have to use a generated App Password:

For AT&T: Search for AT&T Create a secure mail key

For Yahoo: Search for Yahoo Generate and manage 3rd-party app passwords

Answer 1

An .ost file cannot simply be changed into a .pst file. They serve different purposes in Outlook.

.ost is the offline cache used by Exchange, IMAP, and similar accounts.
.pst is an Outlook Data File used for local storage, export, backup, or POP data.

For Classic Outlook on Windows 11 with Microsoft 365, the supported options are:

Change the location of the .ost file by creating a new Outlook profile and selecting a different .ost path during setup.
- In Control Panel > Mail > Show Profiles > Add
- Create the new profile
- After Outlook finds the account, select Change account settings
- Go to More Settings > Advanced > Outlook Data File Settings
- Select Browse and choose an existing .ost file or specify a new location for a new .ost file
- Finish setup, then in Mail, select Always use this profile and choose the new profile
Use the ForceOSTPath registry value to set a different .ost location for a new Outlook profile. Warning: Editing the registry can cause serious problems if done incorrectly.
- Open Run, type regedit, and select OK
- Go to HKEY_CURRENT_USER\Software\Microsoft\Office\xx.0\Outlook
- Create a new Expandable String Value named ForceOSTPath
- Set its value to the full folder path where the .ost file should be stored, such as D:\MyOST
- This works only for a new Outlook profile
If the goal is to store or back up mail in a .pst file, export mailbox data from Classic Outlook:
- File > Open & Export > Import/Export
- Export to a file > Outlook Data File (.pst)
- Select the account, keep Include subfolders selected, choose where to save the .pst, then finish
If a .pst file already exists and the goal is to open it in Outlook, use:
- File > Open & Export > Open Outlook Data File

A .pst file can be opened alongside the mailbox, but it does not replace the .ost inbox file for an Exchange or IMAP account.