Outlook PST file size limit is 50 GB

Outlook PST file size limit is 50 GB.

That is the plain answer, and it is the one that matters first. In current Outlook versions, the default limit for a PST file is 50 GB, and the same 50 GB limit also applies to OST files in the modern setup people usually mean when they ask this question.

That sounds neat on paper. Mail never stays neat for long. A PST file is just Outlook’s local storage file. It holds mail, folders, contacts, and other saved items on the machine. Once it grows too large, Outlook starts to complain, then to slow down, and then to stop adding more data.

I care less about the number than about what it means in practice. A mailbox export that finishes is not the same thing as a clean move. If the file lands near the limit, the work is not really done. The file still needs room to breathe. Outlook is not fond of a stuffed suitcase. Neither am I.

The useful part is simple. Outlook 2010 and later moved to a larger file format that supports much bigger files than the old 2 GB limit from long ago. The default ceiling for that newer format is 50 GB. Microsoft also says that this limit can be changed through registry settings, but that is a separate administrative choice, not the normal starting point.

That second point matters because people often mix up three different things. There is the old PST format, the current PST format, and the OST file that Outlook uses for offline mail. The old ANSI PST format was tiny by modern standards and should not be confused with the newer Unicode format. The newer format is the one tied to the 50 GB default.

OST files confuse people too. An OST file is Outlook’s local copy of a server mailbox. The mailbox can be larger than the local OST limit. That does not mean the OST grows forever. The local file still has its own ceiling. So a big hosted mailbox does not remove the local file limit. The server and the local file are not the same thing, and Outlook treats them that way.

There is one honest wrinkle here. The 50 GB figure is the default and common limit, but it is not the only number that can exist. Microsoft documents that the size limit can be raised or lowered with registry settings. That means the real limit on a given computer can vary. It depends on version, policy, and how Outlook was set up. So when someone asks for the Outlook file size limit, 50 GB is the right short answer, but it is not the last word in every environment.

That uncertainty is normal. Email systems love exceptions. Group policy can change behavior. Older profiles can carry older settings. Add-ins can make a bad day worse. Outlook still wants its files to stay within sane bounds, and 50 GB is the common line in the sand.

I prefer that line for one simple reason. Bigger is not safer. A huge PST file is harder to move, slower to open, and more annoying to repair if something goes wrong. The risk is not that the number exists. The risk is pretending the number does not matter until Outlook starts groaning at it.

So the answer is clear. Outlook PST file size limit is 50 GB, by default, in modern Outlook versions. That is the number most people need when they are checking space, planning a migration, or trying to understand why a file export hit a wall. If the file is close to that limit, the next question is not theory. It is whether every message, folder, and contact still survives the move intact.

That is the line I trust. An export is not finished when Outlook says it is. It is finished when the mail still opens cleanly afterward, with the pieces still in place. That is the whole point of the format, and the part people remember when the inbox has to move again.

The Migration Brief keeps that same focus. One practical fix, one file format explained, and one safer way to move your mail.