How to Open and Split an Oversized PST File (45GB or Larger)

Why a Large PST File in Outlook Becomes a Problem

Outlook’s file contains mail, contacts, calendars, and attachments. When that file gets larger, there’s more data to move when Outlook is indexing, searching, compacting, and so on. And in the event of a log-on interruption on a large file, there’s more data to be corrupted.

The format decides the ceiling:

PST format	Outlook versions	Size limit
ANSI	Outlook 97 to 2002	2 GB
Unicode	Outlook 2003 and 2007	20 GB (default)
Unicode	Outlook 2010 and later	50 GB (default)

The 50 GB ceiling in current versions is a default, but administrators can bypass it by increasing the MaxLargeFileSize and WarnLargeFileSize registry values. However, this does not necessarily solve performance issues related to large data sizes. One might be looking for information about this article if one has a PST file close to the default limit or one experiences performance issues while dealing with large amounts of data.

A few signs that a file needs attention:

• Outlook takes several minutes to start or stops responding while loading the profile
• Folder switching and search lag noticeably
• New mail fails to save to the data file
• Scanpst or Outlook reports errors when opening it

If errors appear at this stage, repair the file first. Our guide on fixing Outlook PST error 0x80040116 walks through that step, and it should be done before any splitting attempt.

How to Open Oversized Large PST File Manually

You have two practical routes, and the right one depends on the file’s condition.

Open Large PST file in Outlook

1. Go to File > Open & Export > Open Outlook Data File.
2. Select the PST file and click OK.
3. Then, just wait for the folders to show up in the navigation pane.

This is the case for a healthy file and lots of memory. You have to wait a long time. Outlook can look like it’s frozen while reading the folder structure on a file close to 50 GB, and you need a working profile to do anything at all.

How to Split a Large PST File Manually

Outlook PST file splitting does not have one button, but there are three built-in approaches to address most cases. Decide which method suits your mail organization structure best.

Method 1: Create a new PST and move folders

This method provides the most control.

1. Choose Home > New Items > More Items > Outlook Data File, and name the new PST.
2. Drag such large project or client folders as a whole from the old file into the new one;
3. Verify that the data you’ve copied exists in the new PST and that you’ve backed up your original file before you delete anything from it.
4. After you’ve done that, delete the originals if you can, then empty the Deleted Items folder. Right-click the old data file. Choose Data File Properties > Advanced > Compact Now.

The last step matters. Deleting items doesn’t shrink the file on disk until compaction runs.

Method 2: Export with a filter

1. Open File > Open & Export > Import/Export.
2. Now choose to Export to a file, then Outlook Data File (.pst).
3. Then choose the folder to be exported, and tick Include subfolders.
4. Apply a filter by clicking the Filter button, and then close the wizard.

Run it several times with different filters to carve the source into smaller sets.

Where Manual Methods Fall Short

The manual steps to Split Oversized large PST file data work, but their costs grow with file size.

Factor	Manual splitting
Outlook dependency	Requires a working, correctly configured profile
Time	Slow on 50 GB or larger files, with repeated waits
Risk	A hang or crash mid-process can leave partial files
Control	Limited filtering, no preview of what goes where
Repeat work	Each new split means redoing the wizard steps

How to Open and Split an Oversized PST File Using DRS Softech

If the default methods of Outlook are not suitable for you and take too much time, DRS Softech PST Viewer Tool is an appropriate solution for opening, viewing, and splitting huge PST files. This tool allows you to open PST files without an Outlook profile, preview emails and attachments, search the desired mailbox, apply filters, and split PST files when exporting mailbox data to save time and space.

Dedicated Tool to Open Large PST Files:

1. Download the tool to load your PST files. Expand the folder structure and preview the large PST files.
2. Choose the recovery modes and saving formats, and use advanced features.
3. Define the path to save the file and click the Save button to start the recovery process.

Steps to Split an Oversized PST File

1. Launch the Dedicated Tool.
2. Add the large PST file and preview its contents.
3. Select PST as the output format.
4. Enable the Split PST File and set the desired options.
5. Set the output folder and click the Export button.
6. After the export process, check the created PST files and their report.

What If a PST File Gets Corrupted?

A large PST file is not necessarily corrupt. But PST file corruption can happen due to unexpected Outlook closing or file system failures. If the file is corrupted, repair a corrupted Outlook PST file using this guide before splitting.

Conclusion

Opening and splitting an Oversized PST File depends on its size and state. Outlook’s built-in archive, move, and export methods can help, but they are often time-consuming and require a working profile. The Dedicated Tool can be used to open PST files without Outlook, preview emails and attachments, apply filters, and even split files while exporting. A mailbox needs to be checked before splitting; the original PST file must be backed up before deleting any data; and the output files have to be validated before deleting the source data.

Frequently Asked Questions