Send and receive dies with a code, or Outlook pops up a plain warning that the file is full. The wording tells you which wall you hit - this page decodes each one.
Outlook does not have one single 'PST full' message - it has several, and they do not all mean the same thing. Some mean your local data file hit its size limit. One famous code can also mean your server mailbox is full, which no registry fix will cure. Read your exact wording below before changing anything.
This is the classic store-full code. It appears during send and receive when the store Outlook is writing to cannot accept more data. For a POP account or a local archive, that store is your PST, and the size-limit fix applies. For an Exchange or Microsoft 365 account, the same code can appear when the server mailbox quota is full - check the mailbox size in webmail or ask your admin. Registry values cannot raise a server quota; only deleting mail or a bigger quota can.
The plain popup - 'The file C:\Users\...\Outlook.pst has reached its maximum size. To reduce the amount of data in this file, select some items that you no longer need, and then permanently delete them' - is unambiguously your local PST. Outlook even names the file. This is the limit the video's one click script raises: 50 GB on modern Outlook, 20 GB on 2003/2007 Unicode files, and a hard 2 GB if the named file turns out to be an old ANSI file.
Outlook actually has two thresholds. WarnLargeFileSize is where warnings start and new content begins to be refused gracefully; MaxLargeFileSize is the absolute top. By default the warn value sits at about 95 percent of the maximum - 47.5 GB against a 50 GB limit. That is why Outlook can feel 'suddenly' full at 47-48 GB on a file everyone believes holds 50. When you raise the maximum, always raise the warn value with it, keeping the same 95 percent gap.
Open File - Account Settings - Data Files - Open File Location and look at the actual PST size on disk. If the file is nowhere near its limit, the error is probably the server quota, a nearly full disk drive, or a damaged file - not the size limit. If the file is at or near the limit, proceed in this order: back the file up, raise the limit with the script or by hand, then immediately archive and compact so you do not land here again next month. Remember what the raise really is: it only moves the wall - an oversized PST stays slower and corrupts more easily, so the registry change is a bridge, not a cure.
The video shows the size-limit fix itself - the one click registry script raising the PST ceiling so Outlook works again.
Watch Full VideoBecause of the warning threshold. Outlook starts enforcing at WarnLargeFileSize, which defaults to about 95 percent of MaxLargeFileSize - roughly 47.5 GB against the 50 GB maximum. Raise both values together and keep the same proportion.
Most likely your server mailbox quota (Exchange, Microsoft 365 or IMAP) is full, or the disk drive holding the data file is out of space. Check the mailbox in webmail and the free space on the drive before touching registry values.
Yes, and it is the healthier fix - but with a catch: deleting mail does not shrink the PST file on disk until you also empty Deleted Items and run Compact Now. Deleting alone frees logical space inside the file; compacting returns the space to Windows.