If your PST is an old ANSI file, the 50 GB conversation is not yours. Your wall is 2 GB, it is built into the format, and here is the way out.
Some PST files in service today were born in the Outlook 97-2002 era, and they carry that era's format - ANSI. The ANSI format physically cannot grow past about 2 GB. Worse, it does not stop gracefully at the wall: files that reach it often start corrupting, losing folder structure and refusing to open. This is the one PST size problem where the registry fix from the video genuinely cannot help, and it is important to know that before you waste an afternoon on it.
Go to File - Account Settings - Data Files, select the file, and open Settings. A Unicode file reads 'Outlook Data File'; an ANSI file reads 'Outlook 97-2002 Data File'. Also watch the symptoms: the file stalls just under 2 GB, send and receive fails near that size, and folders start misbehaving. Do not keep working in a full ANSI file while you plan - every additional item increases the corruption risk.
ANSI files do have registry values - MaxFileSize and WarnFileSize in the same PST key - but they only adjust where Outlook starts warning below the wall. The wall itself, about 2 GB, is a limit of the file format's internal addressing. Typing 102400 into an ANSI value changes nothing; the file cannot physically hold it. Anyone selling you a tool that 'unlocks' an ANSI PST past 2 GB is selling you a corruption.
The durable fix: create a new Unicode Outlook Data File (Data Files - Add), then move your mail into it folder by folder - drag folders in the folder pane, or export from the old file and import into the new one with File - Open and Export - Import/Export. Move Calendar and Contacts too, not just mail. Set the new file as the default delivery location for POP accounts, work from it for a few days, and only then archive the old ANSI file away as a read-only souvenir. Work on a copy of the ANSI file if it is already unstable.
A file already past the wall may refuse the move. Microsoft's last-resort answer is the oversized PST crop tool (PST2GB), and honesty matters here: it works by truncating - cutting the file down to under 2 GB and discarding whatever fell in the cut. You then run ScanPST on the cropped file. Something is usually lost; that is the price of an emergency, and it is exactly why conversion should happen while the file is still healthy. After recovery, treat the incident as the lesson it is: Raising the limit only moves the wall. An oversized PST opens slower, searches slower and corrupts more easily, and the repair takes longer the bigger the file gets. The registry change is a bridge that buys you time - the real cure is archiving old mail out, compacting, and keeping every PST at a sensible size. On a converted Unicode file, those habits come with a 50 GB ceiling instead of a 2 GB cliff.
Once your mail lives in a modern Unicode PST, the video's one click script can raise its limit any time you need headroom.
Watch Full VideoUsually by carrying the same data file forward through upgrades for many years, or restoring an old backup. Outlook happily opens the old format forever - it just never upgrades the file's format on its own, so the 2 GB ceiling travels with it.
ScanPST repairs structural errors, but it cannot shrink an oversized file back under the format limit or make the format hold more. An oversized ANSI file needs the crop tool first (with data loss) and then ScanPST - or better, recovery from a backup taken while the file was still healthy.
Keep it, closed and backed up, until the new Unicode file has run cleanly for a few weeks and you have verified old mail, calendar and contacts all moved. Then archive it like any old document - it costs a couple of gigabytes to keep the safety net.