Remove limit for Outlook OST and PST files


Outlook limits the default size for PST Files and OST Files to 50 GB. The size is determined by the registry value in the registry, the maximum can be increased to about 4 PB (4096 TB).

In Outlook 2003 and Outlook 2007, the maximum recommended size of a PST Data File and an OST Data File was limited to 20 GB.

Outlook 2010, 2013, 2016, 2019, and Microsoft 365 set this recommended limit to 50 GB.

How to increase the maximum file size of a PST Data File ?

To increase the maximum size of PST files and OST files in Outlook, the values must be created and set under the following key in the registry.

Outlook 2003
Outlook 2007
Outlook 2010
Outlook 2013
Outlook 2016 / Outlook 2019 / Microsoft 365

Increase Size of Outlook PST Data File and OST Data File

The following 2 new DWORD values must be created or set, to increase the Outlook Data File limit.

  • WarnLargeFileSize
    Do not set this higher than 4090445042 (decimal) or f3cf3cf2 (hexadecimal)
  • MaxLargeFileSize
    Do not set this higher than 4294967295 (decimal) or ffffffff (hexadecimal)

Run REG ADD in Command Prompt

Opening a command prompt by pressing the Win+Rcmd and run the following two lines.

REG ADD "HKCU\SOFTWARE\Microsoft\Office\16.0\Outlook\PST" /v "WarnLargeFileSize" /t REG_DWORD /d "4090445042" /f

REG ADD "HKCU\SOFTWARE\Microsoft\Office\16.0\Outlook\PST" /v "MaxLargeFileSize" /t REG_DWORD /d "4294967295" /f

Lines with Copy Paste run in the Command Prompt.

The first value WarnLargeFileSize indicates how many MB a user can write to a pst or ost file before receiving a warning that the file is full.The second value MaxLargeFileSize indicates how many MB the system can write to a pst file or ost file.This value must be at least 5% higher because more than just user data is written to a pst file and an ost file.

Registry Key WarnLargeFileSize MaxLargeFileSize

  Although the registry path is PST, it also applies to OST files.

  If the mailbox is on an Exchange Server or an Office 365 account, the quota must also be increased.

Exchange Mailbox usage Quota settings

  In Outlook 2013 and earlier versions, IMAP accounts also used an Outlook Data File (PST). Starting with Outlook 2016 and Outlook for Microsoft 365, IMAP accounts use Offline Outlook Data Files (OST).

Outlook offline data file (OST)

Most account types, e.g. Accounts such as IMAP accounts, Microsoft 365 accounts, Exchange accounts, and use an Offline Outlook Data File (OST) to keep a synchronized copy of your mailbox information on your local computer.

Outlook Data Files (.pst) created using Outlook 2013 or Outlook 2016 are usually stored in the Documents\Outlook Folder on the computer.

Offline Outlook Data File (OST) from Outlook 2019 and Microsoft 365 is saved under %LOCALAPPDATA% under the path \Users\Username\AppData\Local\Microsoft\Outlook. Most of the data remains on the server. However, all locally stored items should be backed up. For example, Calendar, Contacts, Tasks and all folders are only marked as Local.

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2 thoughts on “Remove limit for Outlook OST and PST files”

  1. I’ve been using the REGISTRY fixes for large file, OST/Exchange related, successfully for years, and for one particular client, with several computers, in several locations, without issue until recently.

    That same client, has an office 2019 install, and every time the OST reached 50GB+ it ‘corrupts’ and is apparently unrecoverable.

    Is this an issue with 2019? Is there something else I can do to resolve this, or is the answer to go back to 2016?

    thank you!

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