So I had to recently Reload a MAC to Windows which went all smoothly. We installed Office 365 and setup the corporate account and left the Machine to download over a weekend. On the following Monday we came in and saw the mailbox download 50 GB worth of mail, so only 46 GB left to go. The following day again 50 GB only.
Went through everything from comparing setting to working machines to making sure the user has internet access just to find out that outlook has a limit on the local size it keeps in the .pst or .ost folder. Such a simple thing that I forgot to check.
This is not New
This is actually not new at all but with Microsoft doing all the hard work for you these days it is very easy to forget. The limit on the local size was limited in Office 97 to Office 2002 by actually hard coding a 2 GB file size limit.
In the Office Versions 2003, 2007 and 2010 the limited was improved to 20 GB with the option change this by making some changes in the Registry.
Office 2013, 2016 and 365 again increased this to 50 GB with the same option to change this by making the changes in the Registry.
The Warning
These limits are not set in place because Microsoft decided to Thumb suck it. It is there for a reason. One of the reasons being this is the optimum size for the file size so that corruption does not occur. The second is the format the various version is built on ANSI (An earlier Outlook format) vs UNICODE (a New Outlook Large Format).
I don’t work with encoding but as far as I can tell is ANSI is limited to the amount of Alphabet’s it can encode and UNICODE can encode all possible Characters.
The Fix
To change the file size limit you need to work in the registry. Please note do not delete anything from there unless you know what you are doing or you want to break your machine for reload. Otherwise follow the below steps Exactly.
Open the registry by pressing the Windows Key and the “r” button on you Keyboard simultaneous, in the run command that opened up type “Regedit” and click “OK”. If it ask for administrator privilege click yes.
If your registry was used before it will be open on the keys that was changed, you will see each key has a little arrow next to it that can expand or close that Section of the registry. We need to browse to the following Registry path:
HKEY_Current_User\Software\Microsoft\Office\XX.X\Outlook\PST
For the XX.X you need to know which version or outlook you are using, below is a list of numbers that correspond the the outlook versions:
| Office Version | Registry Number |
| Office 2003 | 11.0 |
| Office 2007 | 12.0 |
| Office 2010 | 14.0 |
| Office 2013 | 15.0 |
| Office 2016 | 16.0 |
Now you Create two REG_DWORD entries you can use the Tables below to Copy and Past the data.
The Values fill in is the Size you want to have the file to grow to in MB filled in as decimal.
Below example it 100 GB with a 90% warning on file size.
| Name | Type | Data (Decimal) |
| MaxLargeFileSize | REG_DWORD | 102400 |
| WarnLargeFileSize | REG_DWORD | 92160 |
Once you changed the setting you can close Outlook and reopen the effect takes place immediately.